Approximate computation via series

[79/76%]
Show
LaTeX

Evaluate the integral

I=∫01/2sin⁡xx dx I = \int _{0}^{1/2} \frac{\sin x}{x}\, dx

to an accuracy of two decimal places; that is, find a number I∗I^{*} such that ∣I−I∗∣<0.005\left|I-I^{*}\right| < 0.005.

?

Estimate the absolute error of the following approximate formulas:

?
(a)

ex≈1+x+x22!+⋯+xnn!e^{x} \approx 1+x+\dfrac {x^{2}}{2!}+\cdots +\dfrac {x^{n}}{n!} for 0⩽x⩽10 \leqslant x \leqslant 1;

(b)

sin⁡x≈x−x36\sin x \approx x-\dfrac {x^{3}}{6} for ∣x∣⩽12\left|x\right| \leqslant \dfrac {1}{2};

(c)

tg⁡x≈x+x33\tg x \approx x+\dfrac {x^{3}}{3} for ∣x∣⩽0.1\left|x\right| \leqslant 0.1;

(d)

1+x≈1+x2−x28\sqrt{1+x} \approx 1+\dfrac {x}{2}-\dfrac {x^{2}}{8} for 0⩽x⩽10 \leqslant x \leqslant 1.

For what values of xx is the approximate formula

cos⁡x=1−x22 \cos x=1-\frac{x^{2}}{2}

accurate to 0.00010.0001.

?

Using Taylor's formula, compute approximately, and estimate the error:

?
(a)

303\sqrt[3]{30};

(b)

2505\sqrt[5]{250};

(c)

400015\sqrt[15]{4000};

(d)

e\sqrt{e};

(e)

sin⁡18°\sin 18°;

(f)

ln⁡1.2\ln 1.2;

(g)

arctg⁡0.8\arctg 0.8;

(h)

arcsin⁡0.45\arcsin 0.45;

(i)

(1.1)1.2(1.1)^{1.2}.

Compute:

?
(a)

ee to within 10−910^{-9};

(b)

sin⁡1°\sin 1° to within 10−810^{-8};

(c)

cos⁡9°\cos 9° to within 10−510^{-5};

(d)

5\sqrt{5} to within 10−410^{-4};

(e)

log⁡1011\log_{10}11 to within 10−510^{-5}.

Compute

∫01(ex−1)ln⁡1xdx \int _{0}^{1}(e^{x}-1)\ln \dfrac {1}{x} dx

accurate to 10−410^{-4}.

?

For which nn can the inequality

∣ex−∑i=0nxii!∣<0.001(0≤x≤10) \left|e^{x}-\sum _{i=0}^{n} \frac{x^{i}}{i!}\right|<0.001 \quad (0 \leq x \leq 10)

be guaranteed to hold?

?

Using Newton's binomial formula, approximately compute 93\sqrt[3]{9}, and estimate the error when only the first three terms of the expansion are taken.

?

Compute approximately, and estimate the corresponding error:

?
(a)

arctan⁡1.2\arctan 1.2;

(b)

100010\sqrt[10]{1000};

(c)

1e\dfrac {1}{\sqrt{e}};

(d)

ln⁡1.25\ln 1.25.

Using a suitable expansion, compute sin⁡18°\sin 18° accurate to 10−510^{-5}.

?

Using a suitable expansion, compute cos⁡1°\cos 1° accurate to 10−610^{-6}.

?

Using a suitable expansion, compute tan⁡9°\tan 9° accurate to 10−310^{-3}.

?

Using a suitable expansion, compute ee accurate to 10−610^{-6}.

?

Using a suitable expansion, compute ln⁡1.2\ln 1.2 accurate to 10−410^{-4}.

?

From the equality π6=arcsin⁡12\dfrac {\pi }{6}=\arcsin \dfrac {1}{2}, find the number π\pi, accurate to 10−410^{-4}.

?

Using the identity π4=arctan⁡12+arctan⁡13\dfrac {\pi }{4}=\arctan \dfrac {1}{2}+\arctan \dfrac {1}{3}, compute the number π\pi, accurate to 0.0010.001.

?

Using the formula π4=4arctan⁡15−arctan⁡1239\dfrac {\pi }{4}=4\arctan \dfrac {1}{5}-\arctan \dfrac {1}{239}, find the number π\pi, accurate to 10−910^{-9}.

?

Using the formula ln⁡(n+1)=ln⁡n+2(12n+1+13(2n+1)3+⋯ )\ln (n+1)=\ln n+2\left(\dfrac {1}{2n+1}+\dfrac {1}{3(2n+1)^{3}}+\cdots \right), find ln⁡2\ln 2 and ln⁡3\ln 3, accurate to 10−510^{-5}.

?

Use the series expansion of the integrand to compute the value of each of the following integrals, accurate to 0.0010.001:

?
(a)

∫01e−x2 dx\displaystyle \int_{0}^{1} e^{-x^{2}}\, dx;

(b)

∫24e1x dx\displaystyle \int_{2}^{4} e^{\frac{1}{x}}\, dx;

(c)

∫02sin⁡xx dx\displaystyle \int_{0}^{2} \frac{\sin x}{x}\, dx;

(d)

∫01cos⁡x2 dx\displaystyle \int_{0}^{1} \cos x^{2}\, dx;

(e)

∫01sh⁡xx dx\displaystyle \int_{0}^{1} \frac{\operatorname {sh}x}{x}\, dx;

(f)

∫2+∞dx1+x3\displaystyle \int_{2}^{+\infty } \frac{dx}{1+x^{3}};

(g)

∫013dx1−x23\displaystyle \int_{0}^{\frac{1}{3}} \frac{dx}{\sqrt[3]{1-x^{2}}};

(h)

∫01dx1+x4\displaystyle \int_{0}^{1} \frac{dx}{\sqrt{1+x^{4}}};

(i)

∫10100ln⁡(1+x)x dx\displaystyle \int_{10}^{100} \frac{\ln (1+x)}{x}\, dx;

(j)

∫012arctan⁡xx dx\displaystyle \int_{0}^{\frac{1}{2}} \frac{\arctan x}{x}\, dx;

(k)

∫012arcsin⁡xx dx\displaystyle \int_{0}^{\frac{1}{2}} \frac{\arcsin x}{x}\, dx;

(l)

∫01xx dx\displaystyle \int_{0}^{1} x^{x}\, dx.

Find the arc length of a single half-wave of the sine curve y=sin⁡xy=\sin x (0≤x≤π0 \leq x \leq \pi), accurate to 0.010.01.

?

An ellipse has semi-axes a=1a=1 and b=12b=\dfrac {1}{2}; find the arc length of the ellipse, accurate to 0.010.01.

?

A wire is strung between two poles standing a distance 2l=202l=20 meters apart, and the wire hangs in the shape of a parabola. Given that the sag at the lowest point is h=40h=40 centimeters, compute the length of the wire, accurate to 11 centimeter.

?

Using Taylor's formula with the remainder term in Lagrange's form (25), approximately compute (to an accuracy of 10−310^{-3}):

?
(1)

127\sqrt{127}

(2)

834\sqrt[4]{83}

(3)

2505\sqrt[5]{250}

(4)

e3\sqrt[3]{e}

(5)

sin⁡85∘\sin 85^{\circ };

(6)

cos⁡72∘\cos 72^{\circ };

(7)

ln⁡1,3\ln 1,3;

(8)

arctg⁡0,8\operatorname {arctg} 0,8.

Using Taylor's formula (25), estimate the absolute error of the approximate formulas:

?
(1)

ex≈∑k=0nxkk!,0⩽x⩽1e^{x} \approx \sum_{k = 0}^{n} \frac{x^{k}}{k !}, 0 \leqslant x \leqslant 1;

(2)

sin⁡x≈x−x33!+x55!,∣x∣⩽1\sin x \approx x-\frac{x^{3}}{3 !}+\frac{x^{5}}{5 !},\left|x\right| \leqslant 1;

(3)

cos⁡x≈1−x22!+x44!−x66!,∣x∣⩽0,5\cos x \approx 1-\frac{x^{2}}{2 !}+\frac{x^{4}}{4 !}-\frac{x^{6}}{6 !},\left|x\right| \leqslant 0,5;

(4)

tg⁡x≈x+x33,∣x∣⩽0,1\operatorname {tg} x \approx x+\frac{x^{3}}{3},\left|x\right| \leqslant 0,1;

(5)

ln⁡(1+x)≈x−x22+x33−x44,∣x∣⩽0,1\ln (1+x) \approx x-\frac{x^{2}}{2}+\frac{x^{3}}{3}-\frac{x^{4}}{4},\left|x\right| \leqslant 0,1;

(6)

1+x≈1+x2−x28+x316,0⩽x⩽0,2\sqrt{1+x} \approx 1+\frac{x}{2}-\frac{x^{2}}{8}+\frac{x^{3}}{16}, 0 \leqslant x \leqslant 0,2.

Using Taylor's formula (25), compute:

?
(1)

ee to an accuracy of 10−710^{-7};

(2)

10\sqrt{10} to an accuracy of 10−310^{-3};

(3)

sin⁡1∘\sin 1^{\circ } to an accuracy of 10−610^{-6};

(4)

cos⁡5∘\cos 5^{\circ } to an accuracy of 10−510^{-5};

(5)

303\sqrt[3]{30} to an accuracy of 10−410^{-4};

(6)

lg⁡11\lg 11 to an accuracy of 10−410^{-4}.

Compute the integral ∫01sin⁡x22dx\int_{0}^{1} \sin \frac{x^{2}}{2} d x with error less than 10−510^{-5}.

?

Compute the integral ∫01cos⁡x2dx\int_{0}^{1} \cos x^{2} d x to five correct digits

?

Prove that:

?
(1)

0,941<∫0π/3cos⁡xdx<0,9570,941 < \int_{0}^{\pi / 3} \sqrt{\cos x} d x < 0,957;

(2)

0,983<∫0π/3sin⁡xxdx<0,9860,983 < \int_{0}^{\pi / 3} \frac{\sin x}{x} d x < 0,986.

Prove that 0<∫01e−x2dx−2635<0,0050 < \int_{0}^{1} e^{-x^{2}} d x-\frac{26}{35} < 0,005.

?

Prove that ∫π/4π/2sin⁡xxdx≈0,610\int_{\pi / 4}^{\pi / 2} \frac{\sin x}{x} d x \approx 0,610 with error not exceeding 1,5⋅10−31,5 \cdot 10^{-3}.

?

Prove that for 0<z<10 < z < 1, for the integral J=∫0zx3dx1+x4J = \int_{0}^{z} \frac{\sqrt[3]{x} d x}{1+x^{4}} the inequalities 34z4/3−316z16/3<J<34z4/3−316z16/3+328z28/3\frac{3}{4} z^{4 / 3}-\frac{3}{16} z^{16 / 3} < J < \frac{3}{4} z^{4 / 3}-\frac{3}{16} z^{16 / 3}+\frac{3}{28} z^{28 / 3} hold.

?

Compute the integral ∫01sin⁡xxdx\int_{0}^{1} \frac{\sin x}{x} d x with error less than 10−510^{-5}, using Taylor's formula.

?

Compute the integral ∫01/4ln⁡(1+x)xdx\int_{0}^{1 / 4} \frac{\ln (1+x)}{x} dx with error less than 10−410^{-4}, using Taylor's formula.

?

Compute the integral ∫−118+x3dx\int_{-1}^{1} \sqrt{8+x^{3}} d x with error less than 10−410^{-4}, using Taylor's formula.

?

Compute the length of a quarter of the ellipse x2+2y2=2x^{2}+2 y^{2} = 2, using Taylor's formula with three terms.

?
?
(1)

Compute the integral ∫0π/2dx1−0,5sin⁡2x\int_{0}^{\pi / 2} \frac{d x}{\sqrt{1-0,5 \sin^{2} x}}, using Taylor's formula with three terms.

(2)

Prove that the error of the result obtained in part 1) does not exceed 0.03.

Compute the integral ∫011−x24dx\int_{0}^{1} \sqrt[4]{1-x^{2}} d x with error not exceeding 10−310^{-3}.

?

Compute the integral ∫01sin⁡x1+x2dx\int_{0}^{1} \frac{\sin x}{1+x^{2}} d x with error less than 10−310^{-3}.

?

Prove that for any n∈N,n⩾2n \in \mathbb {N}, n \geqslant 2,

an−n−12n2(2n+1)<∫011+xnndx<an a_{n}-\frac{n-1}{2 n^{2}(2 n+1)} < \int _{0}^{1} \sqrt[n]{1+x^{n}} d x < a_{n}

where an=1+1n(n+1)a_{n} = 1+\frac{1}{n(n+1)}.

?

Compute the integral ∫011+x1010dx\int_{0}^{1} \sqrt[10]{1+x^{10}} d x with error not exceeding 10−310^{-3}.

?

Prove that n(ak−3(k−1)32k2)<∫0n1+sin⁡2πxkdx<nakn\left(a_{k}-\frac{3(k-1)}{32 k^{2}}\right) < \int_{0}^{n} \sqrt[k]{1+\sin^{2} \pi x} d x < n a_{k}, where ak=1+1/(4k),n∈N,k∈N,k⩾2a_{k} = 1+1 /(4 k), n \in \mathbb {N}, k \in \mathbb {N}, k \geqslant 2.

?

Prove that 1,0473<∫011+sin⁡4πx3dx<1,06251,0473 < \int_{0}^{1} \sqrt[3]{1+\sin^{4} \pi x} d x < 1,0625.

?

Compute the integral ∫081+sin⁡6πxdx\int_{0}^{8} \sqrt{1+\sin^{6} \pi x} dx with error not less than 10−310^{-3}.

?

Using the corresponding expansions, compute to within 10−410^{-4}:

?
(1)

cos⁡1∘\cos 1^{\circ };

(2)

cos⁡10∘\cos 10^{\circ };

(3)

sin⁡10∘\sin 10^{\circ };

(4)

sin⁡1∘\sin 1^{\circ };

(5)

1303\sqrt[3]{130};

(6)

ln⁡1,2\ln 1,2.

Compute to within 10−310^{-3}:

?
(1)

tg⁡9∘\operatorname {tg} 9^{\circ };

(2)

5003\sqrt[3]{500};

(3)

arctg⁡(π/10)\operatorname {arctg}(\pi / 10);

(4)

683\sqrt[3]{68}

(5)

ln⁡5\ln 5;

(6)

arcsin⁡(1/3)\arcsin (1 / 3).

Compute to within 10−510^{-5}:

?
(1)

sin⁡18∘\sin 18^{\circ };

(2)

ee.

Using the equality π/6=arcsin⁡(1/2)\pi / 6 = \arcsin (1 / 2), compute the number π\pi by means of the Maclaurin series for the function arcsin⁡x\arcsin x to within 10−410^{-4}.

?

Using the equality

π4=4arctg⁡15−arctg⁡1239 \frac{\pi }{4} = 4 \operatorname {arctg} \frac{1}{5}-\operatorname {arctg} \frac{1}{239}

compute the number π\pi to within 10−910^{-9}.

?

Using the Maclaurin series for f(x)f(x), compute the integral ∫01f(x)dx\int_{0}^{1} f(x) d x to within 10−310^{-3}, if:

?
(1)

f(x)=sin⁡xxf(x) = \frac{\sin x}{x}

(2)

f(x)=x3cos⁡xf(x) = \sqrt[3]{x} \cos x

(3)

f(x)=cos⁡x2f(x) = \cos x^{2}

(4)

f(x)=sh⁡xxf(x) = \frac{\operatorname {sh} x}{x}

(5)

f(x)=sin⁡x2f(x) = \sin x^{2}

(6)

f(x)=11+x4f(x) = \frac{1}{\sqrt{1+x^{4}}}.

Compute to within 10−310^{-3}:

?
(1)

∫12exxdx\int_{1}^{2} \frac{e^{x}}{x} d x

(2)

∫24e1xdx\int_{2}^{4} e^{\frac{1}{x}} d x

(3)

∫01/2arctg⁡xxdx\int_{0}^{1 / 2} \frac{\operatorname {arctg} x}{x} d x;

(4)

∫01/3dx1−x23\int_{0}^{1 / 3} \frac{d x}{\sqrt[3]{1-x^{2}}};

(5)

∫510ln⁡(1+x2)xdx\int_{5}^{10} \frac{\ln \left(1+x^{2}\right)}{x} d x;

(6)

∫01/2arcsin⁡xxdx\int_{0}^{1 / 2} \frac{\arcsin x}{x} d x;

(7)

∫2+∞dx1+x3dx\int_{2}^{+\infty } \frac{d x}{1+x^{3}} d x;

(8)

∫01xxdx\int_{0}^{1} x^{x} d x.

References

[deSi04] de Souza P.N., Silva J. Berkeley Problems in Mathematics. 3rd ed., Springer, 2004.
[Dem97] Demidovich B.P. Сборник задач и упражнений по математическому анализу. 13-е изд., Издательство Московского университета / Издательство "ЧеРо", 1997.
[ККЧ+03a] Кудрявцев Л.Д., Кутасов А.Д., Чехлов В.И., Шабунин М.И. Предел. Непрерывность. Дифференцируемость. 2-е изд., ФИЗМАТЛИТ, 2003.
[ККЧ+03b] Кудрявцев Л.Д., Кутасов А.Д., Чехлов В.И., Шабунин М.И. Интегралы. Ряды. 2-е изд., ФИЗМАТЛИТ, 2003.