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Solve the Following Question.(3 Marks)

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Question 13 Marks
Evaluate the following:

If $f ( x )= a + bx +c x^2$, show that $\int_0^1 f(x) d x=\frac{1}{6}\left[f(0)+4 f\left(\frac{1}{2}\right)+f(1)\right]$

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Question 33 Marks
Evaluate the following:

If $\int_a^a \sqrt{x} d x=2 a \int_0^{\pi / 2} \sin ^3 x d x$, find the value of $\int_a^{a+1} x d x$.

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Question 103 Marks
Evaluate : $\int_0^\pi x \cdot \sin ^2 x \cdot d x$
Answer
$
\begin{aligned}
& \text { Consider, I } \quad=\int_0^\pi x \cdot \sin ^2 x \cdot d x \ldots \\
& \mathrm{I}=\int_0^\pi(\pi-x) \cdot[\sin (\pi-x)]^2 x \cdot d x \\
& \mathrm{I}=\int_0^\pi(\pi-x) \cdot \sin ^2 x \cdot d x \\
& \mathrm{I}=\int_0^\pi \pi \cdot \sin ^2 x \cdot d x-\int_0^\pi x \cdot \sin ^2 x \cdot d x \\
& \mathrm{I}=\pi \cdot \int_0^\pi \frac{1}{2}(1-\cos 2 x) \cdot d x-\mathrm{I} \ldots \text { by }(\mathrm{i}) \\
& \mathrm{I}+\mathrm{I}=\frac{\pi}{2} \int_0^\pi(1-\cos 2 x) \cdot d x \\
& 2 \mathrm{I}=\frac{\pi}{2}\left[x-\sin 2 x \cdot \frac{1}{2}\right]_0^\pi \\
& I=\frac{\pi}{4}\left[\left(\pi-\frac{1}{2} \sin 2 \pi\right)-\left(0-\frac{1}{2} \sin 0\right)\right] \\
& =\frac{\pi}{4}[\pi] \quad \because \sin 0=0 ; \sin 2 \pi=0 \\
& =\frac{\pi^2}{4} \\
& \therefore \int_0^\pi x^2 \cdot \sin ^2 x \cdot d x=\frac{\pi^2}{4} \\
\end{aligned}
$
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Question 113 Marks
Evaluate : $\int_1^2 \frac{\log x}{x^2} \cdot d x$
Answer
$
\begin{aligned}
& \text { Let I }=\int_1^2(\log x)\left(\frac{1}{x^2}\right) \cdot d x \\
&=\left[(\log x) \cdot \int \frac{1}{x^2} \cdot d x\right]_1^2-\int_1^2 \frac{d}{d x} \log x \cdot \int \frac{1}{x^2} \cdot d x \cdot d x \\
&=\left[(\log x) \cdot\left(-\frac{1}{x}\right)\right]_1^2-\int_1^2 \frac{1}{x} \cdot\left(-\frac{1}{x}\right) \cdot d x \\
&=\left[-\frac{1}{x} \log x\right]_1^2+\int_1^2 \frac{1}{x^2} \cdot d x \\
&=\left[-\frac{1}{x} \log x\right]_1^2+\left[-\frac{1}{x}\right]_1^2 \\
&=\left[\left(-\frac{1}{2} \log 2\right)-\left(-\frac{1}{1} \log 1\right)\right]+\left[\left(-\frac{1}{2}\right)-\left(-\frac{1}{1}\right)\right] \\
&=-\frac{1}{2} \log 2-0-\frac{1}{2}+1=\frac{1}{2}-\frac{1}{2} \log 2 \\
& \therefore \quad \int_1^2 \frac{1}{x^2}\left(\frac{\log x}{2}(1-\log 2)\right.
\end{aligned}
$
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Question 123 Marks
Evaluate : $\int_0^{\pi / 2} \cos ^3 x \cdot d x$
Answer
Let $\mathrm{I}=\int_0^{\pi / 2} \cos ^3 x \cdot d x$
$
\begin{aligned}
& =\int_0^{\pi / 2} \frac{1}{4}[\cos 3 x+3 \cos x] \cdot d x \\
& =\frac{1}{4}\left[\sin 3 x \cdot \frac{1}{3}+3 \sin x\right]_0^{\pi / 2} \\
& =\frac{1}{4}\left[\left(\frac{1}{3} \sin 3 \frac{\pi}{2}+3 \sin \frac{\pi}{2}\right)-\right.
\end{aligned}
$
$
\left.\left(\frac{1}{3} \sin 3(0)+3 \sin (0)\right)\right]
$
$=\frac{1}{4}\left[\frac{1}{3} \sin \frac{3 \pi}{2}+3 \sin \frac{\pi}{2}-\right.$
$
\left.\frac{1}{3} \sin 0+3 \sin 0\right]
$
$=\frac{1}{4}\left[\frac{1}{3}(-1)+3(1)-0\right]$
$=\frac{1}{4}\left[-\frac{1}{3}+3\right]=\frac{1}{4}\left[\frac{8}{3}\right]=\frac{2}{3}$
$\therefore \quad \int_0^{\pi / 2} \cos ^3 x \cdot d x=\frac{2}{3}$
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Question 133 Marks
Evaluate : $\int_0^{\pi / 2} \sqrt{1-\cos 4 x} \cdot d x$
Answer
Let $\mathrm{I}=\int_0^{\pi / 2} \sqrt{1-\cos 4 x} \cdot d x$
$
\begin{aligned}
\mathrm{I}= & \int_0^{\pi / 2} \sqrt{2 \sin ^2 2 x} \cdot d x \\
& \left(\because 1-\cos \mathrm{A}=2 \sin ^2 \frac{\mathrm{A}}{2}\right) \\
= & \sqrt{2} \cdot \int_0^{\pi / 2} \sin 2 x \cdot d x \\
= & \sqrt{2} \cdot\left[\frac{-\cos 2 x}{2}\right]_0^{\pi / 2} \\
= & \frac{\sqrt{2}}{2} \cdot\left[\cos 2 \frac{\pi}{2}-\cos 0\right] \\
= & -\frac{\sqrt{2}}{2} \cdot[\cos \pi-\cos 0] \\
= & -\frac{\sqrt{2}}{2} \cdot(-1-1)=\sqrt{2} \\
\therefore \quad \int_0^{\pi / 2} & \sqrt{1-\cos 4 x} \cdot d x=\sqrt{2}
\end{aligned}
$
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Question 143 Marks
Evaluate : $\int_1^3 \frac{1}{\sqrt{2+x}+\sqrt{x}} \cdot d x$
Answer
$\begin{aligned} & =\int_1^3\left(\frac{1}{\sqrt{2+x}+\sqrt{x}}\right)\left(\frac{\sqrt{2+x}-\sqrt{x}}{\sqrt{2+x}-\sqrt{x}}\right) \cdot d x \\ & =\int_1^3\left(\frac{\sqrt{2+x}-\sqrt{x}}{2+x-x}\right) \cdot d x \\ & =\frac{1}{2} \cdot \int_1^3(\sqrt{2+x}-\sqrt{x}) \cdot d x \\ & =\frac{1}{2} \cdot\left[\frac{(2+x)^{\frac{3}{2}}}{\frac{3}{2}}-\frac{x^{\frac{3}{2}}}{\frac{3}{2}}\right]_1^3\end{aligned}$
$\begin{aligned} & =\frac{1}{3} \cdot\left[(2+x)^{\frac{3}{2}}-(x)^{\frac{3}{2}}\right]_1^3 \\ & =\frac{1}{3}\left\{\left[(2+3)^{\frac{3}{2}}-(3)^{\frac{3}{2}}\right]-\left[(2+1)^{\frac{3}{2}}-(1)^{\frac{3}{2}}\right]\right\} \\ & =\frac{1}{3}\left\{5^{\frac{3}{2}}-3^{\frac{3}{2}}-3^{\frac{3}{2}}+1^{\frac{3}{2}}\right\} \\ & =\frac{1}{3}\left\{5^{\frac{3}{2}}-2(3)^{\frac{3}{2}}+1\right\} \\ & \therefore \int_1^3 \frac{1}{\sqrt{2+x}+\sqrt{x}} d x=\frac{1}{3}\left[5^{\frac{3}{2}}-2(3)^{\frac{3}{2}}+1\right]\end{aligned}$
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Question 153 Marks
Evalaute : $\int_1^2(2 x+5) d x$
Answer
$
\begin{aligned}
& \text { Given, } \int_1^2(2 x+5) d x=\int_a^b f(x) d x \\
& f(x)=2 x+5 \quad a=1 ; b=2 \\
& \Rightarrow \quad f(a+r h)=f(1+r h) \quad \text { and } \quad h=\frac{b-a}{n} \\
& =2(1+r h)+5 \\
& h=\frac{2-1}{n} \\
& =2+2 r h+5 \\
& =7+2 r h \\
& \therefore \quad n h=1 \\
\end{aligned}
$
We know $\int_a^b f(x) d x=\lim _{n \rightarrow \infty} \sum_{r=1}^n h \cdot f(a+r h)$
$\begin{aligned} \therefore \quad \int_1^2(2 x+5) d x & =\lim _{n \rightarrow \infty} \sum_{r=1}^n h \cdot(7+2 r h) \\ & =\lim _{n \rightarrow \infty} \sum_{r=1}^n\left(7 h+2 r h^2\right) \\ & =\lim _{n \rightarrow \infty}\left(7 h \sum_{r=1}^n 1+2 h^2 \sum_{r=1}^n r\right) \\ & =\lim _{n \rightarrow \infty}\left[7 h \cdot(n)+2 h^2\left(\frac{n(n+1)}{2}\right)\right] \\ & =\lim _{n \rightarrow \infty}\left[7 n h+h^2 n^2\left(1+\frac{1}{n}\right)\right] \\ & =\lim _{n \rightarrow \infty}\left[7(1)+(1)^2\left(1+\frac{1}{n}\right)\right] \\ & =7+1(1+0)=8\end{aligned}$
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Question 203 Marks
Evaluate :

$\int_{\frac{1}{\sqrt{2}}}^1 \frac{\left(e^{\cos ^{-1} x}\right)\left(\sin ^{-1} x\right)}{\sqrt{1-x^2}} \cdot d x$

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Question 273 Marks
Evaluate :

$\int_0^{\frac{1}{\sqrt{2}}} \frac{\sin ^{-1} x}{\left(1-x^2\right)^{\frac{3}{2}}} \cdot d x$

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