Section 4

Change of basis and coordinate system

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Problem 4.1

In the plane, two bases e1,e2\mathbf{e}_{1}, \mathbf{e}_{2} and e1′,e2′\mathbf{e}_{1}^{\prime }, \mathbf{e}_{2}^{\prime } are given. The vectors of the second basis have coordinates (−1,3)(- 1, 3) and (2,−7)(2, - 7) respectively in the first basis.

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(1)

Find the coordinates of a vector in the first basis, if its coordinates α1′,α2′\alpha_{1}^{\prime }, \alpha_{2}^{\prime } in the second basis are known.

(2)

Find the coordinates of a vector in the second basis, if its coordinates α1,α2\alpha_{1}, \alpha_{2} in the first basis are known.

(3)

Find the coordinates of the vectors e1,e2\mathbf{e}_{1}, \mathbf{e}_{2} in the second basis.

Problem 4.2

In space, two bases e1,e2,e3\mathbf{e}_{1}, \mathbf{e}_{2}, \mathbf{e}_{3} and e1′,e2′,e3′\mathbf{e}_{1}^{\prime }, \mathbf{e}_{2}^{\prime }, \mathbf{e}_{3}^{\prime } are given. The vectors of the second basis have coordinates (1,1,1),(−1,−2,−3),(1,3,6)(1, 1, 1), (- 1, - 2, - 3), (1, 3, 6) respectively in the first basis.

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(1)

Find the coordinates of a vector in the first basis, if its coordinates α1′,α2′,α3′\alpha_{1}^{\prime }, \alpha_{2}^{\prime }, \alpha_{3}^{\prime } in the second basis are known.

(2)

Find the coordinates of a vector in the second basis, if its coordinates α1,α2,α3\alpha_{1}, \alpha_{2}, \alpha_{3} in the first basis are known.

(3)

Find the coordinates of the vectors e1,e2,e3\mathbf{e}_{1}, \mathbf{e}_{2}, \mathbf{e}_{3} in the second basis.

Problem 4.3

In the plane, two coordinate systems OO, e1,e2\mathbf{e}_{1}, \mathbf{e}_{2} and O′,e1′,e2′O^{\prime }, \mathbf{e}_{1}^{\prime }, \mathbf{e}_{2}^{\prime } are given. The origin of the second coordinate system has coordinates (−1,3)(- 1, 3) in the first system, and the basis vectors of the second system have coordinates (2,3)(2, 3) and (1,1)(1, 1) respectively in the basis of the first system.

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(1)

Find the coordinates of a point in the first system, if its coordinates x′,y′x^{\prime }, y^{\prime } in the second coordinate system are known.

(2)

Find the coordinates of a point in the second system, if its coordinates x,yx, y in the first coordinate system are known.

(3)

Find the coordinates of point OO in the second system, and the coordinates of the vectors e1,e2\mathbf{e}_{1}, \mathbf{e}_{2} in the basis of the second coordinate system.

Problem 4.4

In space, two coordinate systems O,e1,e2O, \mathbf{e}_{1}, \mathbf{e}_{2}, e3\mathbf{e}_{3} and O′,e1′,e2′,e3′O^{\prime }, \mathbf{e}_{1}^{\prime }, \mathbf{e}_{2}^{\prime }, \mathbf{e}_{3}^{\prime } are given. The origin of the second coordinate system has coordinates (1,1,2)(1, 1, 2) in the first system, and the basis vectors of the second coordinate system have coordinates (4,2,1),(5,3,2),(3,2,1)(4, 2, 1), (5, 3, 2), (3, 2, 1) respectively in the basis of the first system.

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(1)

Find the coordinates of a point in the first coordinate system, if its coordinates x′,y′,z′x^{\prime }, y^{\prime }, z^{\prime } in the second system are known.

(2)

Find the coordinates of a point in the second system, if its coordinates x,y,zx, y, z in the first system are known.

(3)

Find the coordinates of point OO in the second coordinate system, and the coordinates of the vectors e1,e2,e3\mathbf{e}_{1}, \mathbf{e}_{2}, \mathbf{e}_{3} in the basis of the second system.

Problem 4.5

The coordinates x,yx, y of every point of the plane in the coordinate system O,e1,e2O, \mathbf{e}_{1}, \mathbf{e}_{2} are expressed through the coordinates x′,y′x^{\prime }, y^{\prime } of the same point in the system O′,e1′,e2′O^{\prime }, \mathbf{e}_{1}^{\prime }, \mathbf{e}_{2}^{\prime } by the formulas x=2x′−y′+5x = 2x^{\prime } - y^{\prime } + 5, y=3x′+y′+2y = 3x^{\prime } + y^{\prime } + 2.

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(1)

Express the coordinates x′,y′x^{\prime }, y^{\prime } through the coordinates x,yx, y.

(2)

Find the coordinates of the origin OO and the basis vectors e1,e2\mathbf{e}_{1}, \mathbf{e}_{2} of the first coordinate system in the second system.

(3)

Find the coordinates of the origin O′O^{\prime } and the basis vectors e1′\mathbf{e}_{1}^{\prime }, e2′\mathbf{e}_{2}^{\prime } of the second coordinate system in the first system.

Problem 4.6

The coordinates x,y,zx, y, z of every point of space in the coordinate system O,e1,e2,e3O, \mathbf{e}_{1}, \mathbf{e}_{2}, \mathbf{e}_{3} are expressed through the coordinates x′,y′,z′x^{\prime }, y^{\prime }, z^{\prime } of the same point in the system O′,e1′,e2′,e3′O^{\prime }, \mathbf{e}_{1}^{\prime }, \mathbf{e}_{2}^{\prime }, \mathbf{e}_{3}^{\prime } by the formulas x=x′+y′+z′−1,y=−x′+z′+3,z=−x′−y′−2x = x^{\prime } + y^{\prime } + z^{\prime } - 1, y = - x^{\prime } + z^{\prime } + 3, z = - x^{\prime } - y^{\prime } - 2.

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(1)

Express the coordinates x′,y′,z′x^{\prime }, y^{\prime }, z^{\prime } through the coordinates x,y,zx, y, z.

(2)

Find the coordinates of the origin OO and the basis vectors e1,e2\mathbf{e}_{1}, \mathbf{e}_{2}, e3\mathbf{e}_{3} of the first coordinate system in the second system.

(3)

Find the coordinates of the origin O′O^{\prime } and the basis vectors e1′\mathbf{e}_{1}^{\prime }, e2′,e3′\mathbf{e}_{2}^{\prime }, \mathbf{e}_{3}^{\prime } of the second system in the first system.

Problem 4.7

Find the coordinates of a vector in the basis e1(2,3),e2(3,4)\mathbf{e}_{1}(2, 3), \mathbf{e}_{2}(3, 4) in the plane, if its coordinates α1′,α2′\alpha_{1}^{\prime }, \alpha_{2}^{\prime } in the basis e1′(1,−1),e2′(2,−3)\mathbf{e}_{1}^{\prime }(1, - 1), \mathbf{e}_{2}^{\prime }(2, - 3) are known.

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Problem 4.8

Find the coordinates of a vector in the basis e1(1,3,2)\mathbf{e}_{1}(1, 3, 2), e2(−1,1,0),e3(2,−1,1)\mathbf{e}_{2}(- 1, 1, 0), \mathbf{e}_{3}(2, - 1, 1) in space, if its coordinates α1′,α2′,α3′\alpha_{1}^{\prime }, \alpha_{2}^{\prime }, \alpha_{3}^{\prime } in the basis e1′(−1,0,2),e2′(1,1,1),e3′(4,3,−1)\mathbf{e}_{1}^{\prime }(- 1, 0, 2), \mathbf{e}_{2}^{\prime }(1, 1, 1), \mathbf{e}_{3}^{\prime }(4, 3, - 1) are known.

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Problem 4.9

Find the coordinates of a point in the coordinate system O(2,−1)O(2, - 1), e1(1,5),e2(−1,4)\mathbf{e}_{1}(1, 5), \mathbf{e}_{2}(- 1, 4) in the plane, if its coordinates x′,y′x^{\prime }, y^{\prime } in the coordinate system O′(3,2),e1′(1,−1),e2′(4,2)O^{\prime }(3, 2), \mathbf{e}_{1}^{\prime }(1, - 1), \mathbf{e}_{2}^{\prime }(4, 2) are known.

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Problem 4.10

Find the coordinates of a point in the coordinate system O(1,3O(1, 3, 3),e1(3,3,1),e2(3,5,2),e3(1,2,1)3), \mathbf{e}_{1}(3, 3, 1), \mathbf{e}_{2}(3, 5, 2), \mathbf{e}_{3}(1, 2, 1) in space, if its coordinates x′,y′,z′x^{\prime }, y^{\prime }, z^{\prime } in the coordinate system O′(−1,0,2)O^{\prime }(- 1, 0, 2), e1′(1,−2,1),e2′(4,2,1),e3′(2,−1,3)\mathbf{e}_{1}^{\prime }(1, - 2, 1), \mathbf{e}_{2}^{\prime }(4, 2, 1), \mathbf{e}_{3}^{\prime }(2, - 1, 3) are known.

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Problem 4.11

In parallelogram ABCDABCD, point EE lies on diagonal BDBD, with ∣BE∣:∣ED∣=1:2\left|BE\right|:\left|ED\right| = 1: 2. Find the coordinates of a point of the plane in the coordinate system A,AB→,AD→A, \overrightarrow {AB}, \overrightarrow {AD}, if its coordinates x′,y′x^{\prime }, y^{\prime } in the coordinate system E,EC→,ED→E, \overrightarrow {EC}, \overrightarrow {ED} are known.

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Problem 4.12

In parallelogram ABCDABCD, point EE lies on side BCBC, and point FF lies on side ABAB, with ∣BE∣:∣BC∣=1:4,∣BF∣:∣AF∣=2:5\left|BE\right|:\left|BC\right| = 1: 4, \left|BF\right|:\left|AF\right| = 2: 5. Find the coordinates of a point of the plane in the coordinate system C,CE→,CD→C, \overrightarrow {CE}, \overrightarrow {CD}, if its coordinates x′,y′x^{\prime }, y^{\prime } in the coordinate system E,EF→,ED→E, \overrightarrow {EF}, \overrightarrow {ED} are known.

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Problem 4.13

In triangle ABCABC, point DD lies on side BCBC, and point EE lies on the extension of side ACAC beyond point CC, with ∣BD∣:∣DC∣=1:2,∣AC∣:∣CE∣=3:1\left|BD\right|:\left|DC\right| = 1: 2, \left|AC\right|:\left|CE\right| = 3: 1. Find the coordinates of a point of the plane in the coordinate system A,AB→,AC→A, \overrightarrow {AB}, \overrightarrow {AC}, if its coordinates x′,y′x^{\prime }, y^{\prime } in the coordinate system D,DA→,DE→D, \overrightarrow {DA}, \overrightarrow {DE} are known.

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Problem 4.14

In triangle ABCABC, point DD lies on side ACAC, and point EE lies on segment BDBD, with ∣AD∣:∣AC∣=1:3\left|AD\right|:\left|AC\right| = 1: 3, ∣BE∣:∣ED∣=2:3\left|BE\right|:\left|ED\right| = 2: 3. Find the coordinates of a point of the plane in the coordinate system A,AB→,AD→A, \overrightarrow {AB}, \overrightarrow {AD}, if its coordinates x′x^{\prime }, y′y^{\prime } in the coordinate system C,CB→,CE→C, \overrightarrow {CB}, \overrightarrow {CE} are known.

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Problem 4.15

Given a regular hexagon ABCDEFABCDEF. Find the coordinates of a point of the plane in the coordinate system A,AB→,AF→A, \overrightarrow {AB}, \overrightarrow {AF}, if its coordinates x′,y′x^{\prime }, y^{\prime } in the coordinate system CC, CB→,CE→\overrightarrow {CB}, \overrightarrow {CE} are known.

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Problem 4.16

In trapezoid ABCDABCD the diagonals meet at point EE, and the lengths of the bases BCBC and ADAD are in the ratio 2:32: 3. Find the coordinates of a point of the plane in the coordinate system A,AB→A, \overrightarrow {AB}, AD→\overrightarrow {AD}, if its coordinates x′,y′x^{\prime }, y^{\prime } in the coordinate system EE, EA→,EB→\overrightarrow {EA}, \overrightarrow {EB} are known.

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Problem 4.17

In trapezoid ABCDABCD the lengths of the bases BCBC and ADAD are in the ratio 3:43: 4, point EE is the midpoint of base ADAD, and the extensions of the lateral sides meet at point FF. Find the coordinates of a point of the plane in the coordinate system E,EB→E, \overrightarrow {EB}, EC→\overrightarrow {EC}, if its coordinates x′,y′x^{\prime }, y^{\prime } in the coordinate system F,FB→,FC→F, \overrightarrow {FB}, \overrightarrow {FC} are known.

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Problem 4.18

The base of prism ABCDA1B1C1D1ABCDA_{1} B_{1} C_{1} D_{1} is a rhombus with acute angle AA equal to 60∘60^{\circ }. Point KK lies on the extension of edge ABAB beyond point BB, with angle ADKADK right. Find the coordinates of a point of space in the coordinate system A,AB→,AD→A, \overrightarrow {AB}, \overrightarrow {AD}, AA1→\overrightarrow {AA_{1}}, if its coordinates x′,y′,z′x^{\prime }, y^{\prime }, z^{\prime } in the coordinate system K,KA→,KD→,KC1→K, \overrightarrow {KA}, \overrightarrow {KD}, \overrightarrow {KC_{1}} are known.

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Problem 4.19

In triangular prism ABCA1B1C1ABCA_{1} B_{1} C_{1}, point MM is the intersection point of the medians of face A1B1C1A_{1} B_{1} C_{1}. Find the coordinates of a point of space in the coordinate system A,AB→,AC→,AB1→A, \overrightarrow {AB}, \overrightarrow {AC}, \overrightarrow {AB_{1}}, if its coordinates x′,y′,z′x^{\prime }, y^{\prime }, z^{\prime } in the coordinate system A1,A1B‾A_{1}, \overline{A_{1} B}, A1C→,A1M→\overrightarrow {A_{1} C}, \overrightarrow {A_{1} M} are known.

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Problem 4.20

In tetrahedron ABCDABCD, point MM is the intersection point of the medians of face BCDBCD. Find the coordinates of a point of space in the coordinate system A,AB→,AC→,AD→A, \overrightarrow {AB}, \overrightarrow {AC}, \overrightarrow {AD}, if its coordinates x′,y′,z′x^{\prime }, y^{\prime }, z^{\prime } in the coordinate system M,MB→,MC→,MA→M, \overrightarrow {MB}, \overrightarrow {MC}, \overrightarrow {MA} are known.

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Problem 4.21

In a regular hexagonal pyramid SABCDEFSABCDEF with apex SS, point MM is the center of the base. Find the coordinates of a point of space in the coordinate system A,AB→,AF→A, \overrightarrow {AB}, \overrightarrow {AF}, AS→\overrightarrow {AS}, if its coordinates x′,y′,z′x^{\prime }, y^{\prime }, z^{\prime } in the coordinate system S,SC→,SD→,SM→S, \overrightarrow {SC}, \overrightarrow {SD}, \overrightarrow {SM} are known.

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Problem 4.22

Given a parallelepiped ABCDA1B1C1D1ABCDA_{1} B_{1} C_{1} D_{1}. Find the coordinates of a point of space in the coordinate system A,AC→,AB1→A, \overrightarrow {AC}, \overrightarrow {AB_{1}}, AA1→\overrightarrow {AA_{1}}, if its coordinates x′,y′,z′x^{\prime }, y^{\prime }, z^{\prime } in the coordinate system D1,D1D→,D1C1→,D1Bˉ→D_{1}, \overrightarrow {D_{1} D}, \overrightarrow {D_{1} C_{1}}, \overrightarrow {D_{1} \bar{B}} are known

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Problem 4.23

The coordinates x,yx, y of every point of the plane in the first coordinate system are expressed through the coordinates x′,y′x^{\prime }, y^{\prime } of the same point in the second coordinate system by the relations x=a11x′+a12y′+a10,y=a21x′+a22y′+a20x = a_{11} x^{\prime } + a_{12} y^{\prime } + a_{10}, y = a_{21} x^{\prime } + a_{22} y^{\prime } + a_{20}. The first coordinate system is rectangular. Under what necessary and sufficient condition is the second system also rectangular?

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Problem 4.24

The coordinates x,y,zx, y, z of every point of space in the first coordinate system are expressed through the coordinates x′x^{\prime }, y′,z′y^{\prime }, z^{\prime } of the same point in the second coordinate system by the relations

x=a11x′+a12y′+a13z′+a10,y=a21x′+a22y′+a23z′+a20,z=a31x′+a32y′+a33z′+a30. \begin{aligned} & x = a_{11} x^{\prime } + a_{12} y^{\prime } + a_{13} z^{\prime } + a_{10}, \\ & y = a_{21} x^{\prime } + a_{22} y^{\prime } + a_{23} z^{\prime } + a_{20}, \\ & z = a_{31} x^{\prime } + a_{32} y^{\prime } + a_{33} z^{\prime } + a_{30}. \end{aligned}
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(1)

Suppose the first coordinate system is rectangular. Under what necessary and sufficient condition is the second system also rectangular?

(2)

Under what necessary and sufficient condition is the orientation of the bases of the first and second systems the same?

Problem 4.25

In the plane, two rectangular coordinate systems O,e1,e2O, \mathbf{e}_{1}, \mathbf{e}_{2} and O′,e1′,e2′O^{\prime }, \mathbf{e}_{1}^{\prime }, \mathbf{e}_{2}^{\prime } are given. The origin of the second coordinate system has coordinates x0,y0x_{0}, y_{0} in the first system, and the vectors e1′\mathbf{e}_{1}^{\prime } and e2′\mathbf{e}_{2}^{\prime } are obtained from the vectors e1\mathbf{e}_{1} and e2\mathbf{e}_{2} respectively by a rotation through the same angle φ\varphi in the direction of the shortest rotation from e1\mathbf{e}_{1} to e2\mathbf{e}_{2}.

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(1)

Find the coordinates of a point in the first coordinate system, if its coordinates x′,y′x^{\prime }, y^{\prime } in the second system are known.

(2)

Find the coordinates of a point in the second coordinate system, if its coordinates x,yx, y in the first system are known.

(3)

Find the coordinates of point OO in the second coordinate system.

Problem 4.26

In the plane, two rectangular coordinate systems O,e1,e2O, \mathbf{e}_{1}, \mathbf{e}_{2} and O′,e1′,e2′O^{\prime }, \mathbf{e}_{1}^{\prime }, \mathbf{e}_{2}^{\prime } are given. The origin of the second coordinate system has coordinates 1, 3 in the first system, and the vectors e1′\mathbf{e}_{1}^{\prime } and e2′\mathbf{e}_{2}^{\prime } are obtained from the vectors e1\mathbf{e}_{1} and e2\mathbf{e}_{2} respectively by a rotation through the same angle φ\varphi in the direction of the shortest rotation from e1\mathbf{e}_{1} to e2\mathbf{e}_{2}. Find the coordinates of a point in the first coordinate system, if its coordinates x′,y′x^{\prime }, y^{\prime } in the second system are known, taking the angle φ\varphi equal to:

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(1)

60∘60^{\circ }

(2)

135∘135^{\circ }

(3)

90∘90^{\circ }

(4)

180∘180^{\circ }

Problem 4.27

In the plane, two rectangular coordinate systems O,e1,e2O, \mathbf{e}_{1}, \mathbf{e}_{2} and O′,e1′,e2′O^{\prime }, \mathbf{e}_{1}^{\prime }, \mathbf{e}_{2}^{\prime } are given. The origin of the second coordinate system has coordinates x0,y0x_{0}, y_{0} in the first system, and the vectors e1′\mathbf{e}_{1}^{\prime } and −e2′- \mathbf{e}_{2}^{\prime } are obtained from the vectors e1\mathbf{e}_{1} and e2\mathbf{e}_{2} respectively by a rotation through the same angle φ\varphi in the direction of the shortest rotation from e1\mathbf{e}_{1} to e2\mathbf{e}_{2}.

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(1)

Find the coordinates of a point in the first coordinate system, if its coordinates x′,y′x^{\prime }, y^{\prime } in the second system are known.

(2)

Find the coordinates of a point in the second coordinate system, if its coordinates x,yx, y in the first system are known.

(3)

Find the coordinates of point OO in the second coordinate system.

Problem 4.28

In right triangle ABCABC, whose legs have lengths ∣AB∣=3\left|AB\right| = 3 and ∣BC∣=4\left|BC\right| = 4, point DD is the foot of the altitude drawn from the vertex of the right angle. Vectors e1,e2,e1′,e2′\mathbf{e}_{1}, \mathbf{e}_{2}, \mathbf{e}_{1}^{\prime }, \mathbf{e}_{2}^{\prime } have length 1, with e1\mathbf{e}_{1} equally directed with BA→,e2\overrightarrow {BA}, \mathbf{e}_{2} equally directed with BC→,e1′\overrightarrow {BC}, \mathbf{e}_{1}^{\prime } equally directed with AC→,e2′\overrightarrow {AC}, \mathbf{e}_{2}^{\prime } equally directed with DB→\overrightarrow {DB}. Find the coordinates of a point of the plane in the coordinate system B,e1B, \mathbf{e}_{1}, e2\mathbf{e}_{2}, if its coordinates x′,y′x^{\prime }, y^{\prime } in the coordinate system DD, e1′,e2′\mathbf{e}_{1}^{\prime }, \mathbf{e}_{2}^{\prime } are known.

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Problem 4.29

In space, two rectangular coordinate systems O,e1,e2,e3O, \mathbf{e}_{1}, \mathbf{e}_{2}, \mathbf{e}_{3} and O′,e1′,e2′,e3′O^{\prime }, \mathbf{e}_{1}^{\prime }, \mathbf{e}_{2}^{\prime }, \mathbf{e}_{3}^{\prime } are given. The origin of the second coordinate system has coordinates −1,3,5- 1, 3, 5 in the first system. The vector e1′\mathbf{e}_{1}^{\prime } makes angles equal to 60∘60^{\circ } with the vectors e1\mathbf{e}_{1} and e2\mathbf{e}_{2}, and an acute angle with the vector e3\mathbf{e}_{3}. The vector e2′\mathbf{e}_{2}^{\prime } is coplanar with the vectors e1\mathbf{e}_{1} and e2\mathbf{e}_{2} and makes an acute angle with the vector e2\mathbf{e}_{2}. The triples e1,e2,e3\mathbf{e}_{1}, \mathbf{e}_{2}, \mathbf{e}_{3} and e1′,e2′,e3′\mathbf{e}_{1}^{\prime }, \mathbf{e}_{2}^{\prime }, \mathbf{e}_{3}^{\prime } have the same orientation. Find the coordinates of a point of space in the first coordinate system, if its coordinates x′,y′,z′x^{\prime }, y^{\prime }, z^{\prime } in the second system are known.

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Problem 4.30

In space, two rectangular coordinate systems O,e1,e2,e3O, \mathbf{e}_{1}, \mathbf{e}_{2}, \mathbf{e}_{3} and O′,e1′,e2′,e3′O^{\prime }, \mathbf{e}_{1}^{\prime }, \mathbf{e}_{2}^{\prime }, \mathbf{e}_{3}^{\prime } are given. Points OO and O′O^{\prime } are distinct, and the endpoints of the vectors e2\mathbf{e}_{2} and ei′\mathbf{e}_{i}^{\prime }, drawn respectively from points OO and O′O^{\prime }, coincide (i=1,2,3)(i = 1, 2, 3). Find the coordinates of a point of space in the first coordinate system, if its coordinates x′,y′,z′x^{\prime }, y^{\prime }, z^{\prime } in the second system are known.

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