Cardioid and limacon of Pascal

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Find the radius of curvature of the curve given by the following polar equation: the cardioid r=a(1+cos⁡φ)r=a(1+\cos \varphi ).

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From a point AA on a circle of diameter aa, secants are drawn. On each of them, on both sides of the other point of intersection with the circle, segments of length bb are laid off. Find the locus of their endpoints. (Limaçon of Pascal.)

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For n=1n=1 the epicycloid becomes a curve called the cardioid. Show that the equation of the cardioid, in suitably chosen polar coordinates, has the form r=a(1+cos⁡φ)r = a(1+\cos \varphi ).

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Show that the cardioid (see the preceding problem) is a special case of the limaçon of Pascal (see problem 141).

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Find the angle between the tangent and the polar radius of the point of tangency for the following curves:

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(1)

the spiral of Archimedes r=aφr = a \varphi;

(2)

the hyperbolic spiral r=a/φr = a / \varphi;

(3)

the logarithmic spiral r=aebφr = a e^{b \varphi };

(4)

the cardioid r=a(cos⁡φ+1)r = a(\cos \varphi +1);

(5)

the arc of the lemniscate of Bernoulli r2=a2cos⁡2φ,0⩽φ<π/4r^{2} = a^{2} \cos 2 \varphi , 0 \leqslant \varphi < \pi / 4.

Prove that the evolute of a cardioid is also a cardioid.

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Find the area of the figure bounded by the curve:

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(1)

x=acos⁡t,y=bsin⁡tx = a \cos t, \quad y = b \sin t (ellipse);

(2)

x=c2acos⁡3t,y=c2bsin⁡3t,c2=a2−b2x = \frac{c^{2}}{a} \cos^{3} t, \quad y = \frac{c^{2}}{b} \sin^{3} t, \quad c^{2} = a^{2}-b^{2} (evolute of the ellipse);

(3)

x=1−t2(1+t2)2,y=2at(1+t2)2x = \frac{1-t^{2}}{\left(1+t^{2}\right)^{2}}, \quad y = \frac{2 a t}{\left(1+t^{2}\right)^{2}} (limaçon);

(4)

x=r(ncos⁡t−cos⁡nt),y=r(nsin⁡t−sin⁡nt),n−1∈Nx = r(n \cos t-\cos n t), \quad y = r(n \sin t-\sin n t), \quad n-1 \in \mathbb {N} (epicycloid);

(5)

x=r(ncos⁡t+cos⁡nt),y=r(nsin⁡t−sin⁡nt),n−1∈Nx = r(n \cos t+\cos n t), \quad y = r(n \sin t-\sin n t), \quad n-1 \in \mathbb {N} (hypocycloid);

(6)

x=a(1−cos⁡t)cos⁡t,y=a(1−cos⁡t)sin⁡tx = a(1-\cos t) \cos t, \quad y = a(1-\cos t) \sin t (cardioid).

Find the area of the figure bounded by curves given in polar coordinates.

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(1)

r=acos⁡(φ−π/3),φ=0,φ=π2r = \frac{a}{\cos (\varphi -\pi / 3)}, \quad \varphi = 0, \quad \varphi = \frac{\pi }{2};

(2)

r=acos⁡φr = a \cos \varphi;

(3)

r=a(1+cos⁡φ)r = a(1+\cos \varphi ) (cardioid);

(4)

r=b+acos⁡φ,a⩾b>0r = b+a \cos \varphi , a \geqslant b > 0 (limaçon);

(5)

r=asin⁡2φr = a \sin 2 \varphi (find the area of one petal);

(6)

r=acos⁡3φr = a \cos 3 \varphi;

(7)

r=asin⁡5φr = a \sin 5 \varphi;

(8)

r=asin⁡nφ,n∈Nr = a \sin n \varphi , n \in \mathbb {N}

(9)

r=p1+ecos⁡φ,φ=0,φ=φ0,0⩽φ⩽φ0,0<e<1r = \frac{p}{1+e \cos \varphi }, \varphi = 0, \varphi = \varphi_{0}, 0 \leqslant \varphi \leqslant \varphi_{0}, 0 < e < 1 (ellipse);

(10)

r=p1+ecos⁡φ,φ=0,φ=φ0,0⩽φ⩽φ0,e>1,ecos⁡φ0>−1r = \frac{p}{1+e \cos \varphi }, \varphi = 0, \varphi = \varphi_{0}, 0 \leqslant \varphi \leqslant \varphi_{0}, e > 1, e \cos \varphi_{0} > -1 (hyperbola);

(11)

r=11+cos⁡2φ,φ=0,φ=π4r = \frac{1}{\sqrt{1+\cos^{2} \varphi }}, \varphi = 0, \varphi = \frac{\pi }{4}

(12)

r=14−3cos⁡2=,φ=0,φ=π2r = \frac{1}{\sqrt{4-3 \cos^{2}}} = , \varphi = 0, \varphi = \frac{\pi }{2};

(13)

r=2φarccos⁡(φ2−1),φ=1,φ=3/2r = 2 \sqrt{\varphi \arccos \left(\varphi^{2}-1\right)}, \varphi = 1, \varphi = \sqrt{3 / 2};

(14)

r=sin⁡φcos⁡φ,φ=0,φ=π6r = \frac{\sin \varphi }{\sqrt{\cos \varphi }}, \varphi = 0, \varphi = \frac{\pi }{6}.

Find the area of the figure bounded by:

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(1)

the outer loop of the limaçon ∣r−1cos⁡φ∣=1\left|r-1 \cos \varphi \right| = 1;

(2)

its inner loop.

Inside a circle of radius RR there is a point AA at distance aa from the center. A curve is formed by the feet of the perpendiculars dropped from the point AA onto the tangents to the circle. Find the area of the figure bounded by this curve.

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Find the length of the arc of the curve:

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(1)

r=asin⁡φr = a \sin \varphi

(2)

r=aekφ,φ1⩽φ⩽φ2r = a e^{k \varphi }, \quad \varphi_{1} \leqslant \varphi \leqslant \varphi_{2} (logarithmic spiral);

(3)

r=a(1−cos⁡φ)r = a(1-\cos \varphi ) (cardioid);

(4)

r=2(1+cos⁡φ),r⩽1r = 2(1+\cos \varphi ), \quad r \leqslant 1;

(5)

r=a(1−sin⁡φ),−π/2⩽φ⩽−π/6r = a(1-\sin \varphi ), \quad -\pi / 2 \leqslant \varphi \leqslant -\pi / 6;

(6)

r=ath⁡(φ/2),0⩽φ⩽φ0r = a \operatorname {th}(\varphi / 2), \quad 0 \leqslant \varphi \leqslant \varphi_{0}.

Find the volume of the solid formed by rotating Pascal's limaçon around the polar axis:

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(1)

r=acos⁡φ+l,l<ar = a \cos \varphi +l, l < a (outer loop);

(2)

r=acos⁡φ−l,l<ar = a \cos \varphi -l, l < a (inner loop);

(3)

r=acos⁡φ+l,l⩾ar = a \cos \varphi +l, l \geqslant a.

Find the volume of the solid formed by rotating the cardioid r=a(1+cos⁡φ)r = a(1+\cos \varphi ) around the line rcos⁡φ=−a/4r \cos \varphi = -a / 4.

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(Limaçon of Pascal.) On a circle, two diametrically opposite points OO and AA are taken, with ∣OA∣=a\left|O A\right| = a. A ray rotates about the point OO. Let BB be the variable point of intersection of the line containing this ray with the circle. On the line OBO B, from the point BB in the direction of the ray, a segment BMB M of length bb is laid off. Write, in generalized polar and rectangular coordinates, the equation of the curve traced by the point MM as the ray rotates, taking the point OO as the origin and the direction OA→\overrightarrow {O A} as the positive direction of the axis OxO x.

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Indicate the angle at which the limaçon of Pascal from the preceding problem intersects the axis OxO x at the origin

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(1)

for b<ab < a;

(2)

for b=ab = a?

Prove that the locus of the feet of the perpendiculars dropped from a given point onto the tangents to a given circle is a limaçon of Pascal.

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(Cardioid.) A circle of radius aa is given, and on it two diametrically opposite points OO and AA. A ray rotates about the point OO. Let the line containing this ray intersect the circle at a variable point BB. On this line, from the point BB in the direction of the ray, a segment BMB M equal to the diameter of the circle is laid off. Write, in generalized polar and rectangular coordinates, the equation of the curve traced by the point MM as the ray rotates, taking the point OO as the origin, and the ray OAO A as the positive direction of the axis OxO x.

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Prove that the following curves are cardioids:

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(1)

the locus of points symmetric to a point AA, lying on a given circle, with respect to all possible tangents to this circle;

(2)

the locus of the feet of the perpendiculars dropped from a point AA, lying on a given circle, onto all possible tangents to this circle.

A circle is given, and on it a point AA. Prove that the circles passing through the point AA, whose centers lie on the given circle, sweep out a region bounded by a certain cardioid.

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References

[Dem97] Demidovich B.P. Сборник задач и упражнений по математическому анализу. 13-е изд., Издательство Московского университета / Издательство "ЧеРо", 1997.
[ГюКу03] Гюнтер Н.М., Кузьмин Р.О. Сборник задач по высшей математике. 13-е изд., Издательство «Лань», 2003.
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[ККЧ+03b] Кудрявцев Л.Д., Кутасов А.Д., Чехлов В.И., Шабунин М.И. Интегралы. Ряды. 2-е изд., ФИЗМАТЛИТ, 2003.
[Сми16] Смирнов Ю.М. Сборник задач по аналитической геометрии и линейной алгебре. МЦНМО, 2016.