11. Answer: (d) log (10x + x10) + c.
Explanation: Given:
\(\int\frac{(10x^9+10x\,In\,10)dx}{(x^{10}+10^x)}\)
To evaluate
take \(y=x^{10}+10^x\)
\(\frac{dy}{dx}=10x^9+10x\,In\,10\)
\(dy=(10x^9+10^x\,In\,10)\;dx\)
\(\therefore\) \(I=\int\frac{dy}y=In\,y\)
Hence, the correct answer is \(In|(x^{10}+10^x)|\)
12. Answer: (b) tan (xex) + c
Explanation: Let \(I=\int\frac{e^x(1+x)}{cos^2(xe^x)}dx\)
Put \(x.e^x\) = t
Diff.w.r.t..x
\(\therefore\) \(x.e^x+e^x.1=\frac{dt}{dx}\)
\(\therefore\) \(e^x(1+x)dx=dt\)
\(\therefore I=\int\frac{dt}{cos^2t}=\int sec^2tdt\)
\(\therefore\) tan t + c
\(=tan(x.e^x)+e\)
13. Answer: (a) 1/6
Explanation: Given :
\(\therefore\) \(\int\frac1{(x^2+4)(x^2+9)}dx\) \(=A\,tan^{-1}\frac x2+B\,tan^{-1}\frac x3+C\;\;...(i)\)
\(\frac1{AB}=\frac1{B-A}(\frac1{A}-\frac1{B})\)
\(\therefore\) \(\int\frac1{(x^2+4)(x^2+9)}dx\) \(=\int\frac1{5}(\frac1{x^2+4}-\frac1{x^2+9})dx\)
\(=\frac1{5}\left[\frac1{2}tan^{-1}\frac x{2}-\frac1{3}tan^{-1}\frac x{3}\right]+C\)
\(=\frac1{10}tan^{-1}\frac x{2}-\frac1{15}tan^{-1}\frac x{3}+C\)
Comparing above equation with (i) we get
A = \(\frac1{10}\) and B = \(-\frac1{15}\)
\(\therefore\) A - B \(=\frac{1}{10}+\frac{1}{15}=\frac{5}{30}=\frac{1}{6}\)
14. Answer: (a) extan-1x+C
Explanation: \(\int\frac{e^x(x^2tan^{-1}x+tan^{-1}x+1)}{x^2+1}dx\) \(=\int\frac{e^x[(x^2+1)\,tan^{-1}x)+1]}{x^2+1}dx\)
\(=\int e^x(tan^{-1}x+\frac{1}{1+x^2})dx\) \(=e^xtan^{-1}x+c\)
Note : \(\int\) \(e^x\)[f(x) + f'(x)] dx = \(e^x\) f(x) + c
Here f(x) = \(tan^{-1}x\)
15. Answer: (c) a = -1/10, b = 2/5
Explanation: \(I=\int\frac{dx}{(x+2)(x^2+1)}\)
\(\frac{1}{(x+2)(x^2+1)}=\frac A{x+2}+\frac{Bx+C}{x^2+1}\)
\(\Rightarrow\) 1 = A(\(x^2\)+1) + (Bx+C) (x+2)
\(\Rightarrow\) 1 = (A+B)\(x^2\) + (2B+C)x + A + 2C
Comparing coefficients, we get
A+B = 0, A+2C = 1, 2B+C = 0
Solving we get A = \(\frac15\), B = \(-\frac15\) and C = \(\frac25\)
\(\therefore\) \(\int\frac{dx}{(x+2)(x^2+1)}\)
\(=\frac15\int\frac1{x+2}dx+\int\cfrac{-\frac{1}{5}x+\frac{2}{5}}{x^2+1}dx\)
\(=\frac15\int\frac1{x+2}dx-\frac1{10}\int\frac{2x}{1+x^2}dx+\frac15\int\frac{2}{1+x^2}dx\)
\(=\frac15log|x+2|-\frac1{10}log|1+x^2|\) \(+\frac25tan^{-1}x+C\)
\(=a\,log|1+x^2|+b\,tan^{-1}x\) \(+\frac15\,log|x+2|+C\) (given)
\(\therefore\) \(a=\frac{-1}{10},b=\frac25\)
16. Answer: (a) 1/3 ex^3+C
Explanation: \(\int x^2e^xdx\)
Let \(x^3\) = t
\(\Rightarrow\) \(3x^2=\frac{dt}{dx}\)
\(\Rightarrow dx=dt/3x^2\)
\(\therefore\) \(\int x^2\times e^t\times\frac{dt}{3x^2}\)
\(=\frac13\int e^tdt\)
\(=\frac13e^t+c\)
\(=\frac13\times e^{x^3}+c\)
17. Answer: (b) ex sec x + c
Explanation: Let \(I=\int e^x\) sec x (1+tan x)dx
\(=\int e^x\) (sec x + sec x tan x)dx
Also, let sec x = f(x)
\(\Rightarrow\) sec x tan x = f'(x)
We know that,
\(\int e^x\) {f(x) + f'(x)} = \(e^x\) f(x) + C
\(\therefore\) I = \(e^x\) sec x + C
18. Answer: (a) (x + 1)tan-1 √x – √x + c
Explanation: \(\int tan^{-1}\;\sqrt xdx\)
Apply integration by parts
\(x\int tan^{-1}\;\sqrt x-\int\frac x{2(1+x)\sqrt x}dx\)
\(x\int tan^{-1}\;\sqrt x-\frac12\int\frac{\sqrt x}{1+x}dx\)
Let \(\sqrt x\) = t
\(\frac{dx}{2\sqrt x}=dt\)
dx = 2tdt
\(=x\,tan^{-1}\;\sqrt x-\int\frac{t^2}{1+t^2}dt\)
\(=x\,tan^{-1}\;\sqrt x-\int dt+\int\frac{1}{1+t^2}dt\)
\(x\,tan^{-1}\;\sqrt x-\sqrt x+tan^{-1}\sqrt x+c\)
\(=(x-1)tan^{-1}\sqrt x-\sqrt x+c\)
19. Answer: (a) ex cosx + C
Explanation: since \(\int e^x\) (f(x) + f'(x))dx = \(e^x\) f(x) + C
Here f(x) = cos x, f'(x) = -sin x.
So, \(\int e^x\) (cos x - sin x)dx = \(e^x\) cos x + C
20. Answer: (d) -2 ≤ a ≤ 4
Explanation: as \(\int_0^axdx\) ≤ a + 4
⇒ a2/2 ≤ a + 4
⇒ a2 – 2a — 8 ≤ 0
⇒ (a – 1)2 ≤ (3)2
⇒ -3 ≤ a – 1 ≤ 3
⇒ -2 ≤ a ≤ 4
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