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If int(0)^(pi)xf(sinx)dx=A int(0)^(pi//2...

If `int_(0)^(pi)xf(sinx)dx=A int_(0)^(pi//2) f(sinx)dx`, then A is

A

`2pi`

B

`pi`

C

`pi//4`

D

0

Text Solution

Verified by Experts

The correct Answer is:
B
Let `I=overset(pi)underset(0)int xf(sinx)dx`.
`I=overset(pi)underset(0)int(pi-x)f(sin(pi-x))dx[:'overset(a)underset(0)intf(x)dx=overset(a)underset(0)intf(a-x)dx]`
`rArr I=pi overset(pi)underset(0)int f(sinx)dx-1`
`rArr I=(pi)/(2)overset(pi)underset(0)int f(sin x)dx`
`rArr I=(pi)/(2)xx2overset(pi//2)underset(0)int f(sin x)dx [:'overset(2a)underset(0)int f(x)dx=2overset(a)underset(0)int f(x)dx" if ",f(2a-x)=f(x)]`
`rArrI=pi overset(pi//2)underset(0)int f(sinx)`
`:.overset(pi)underset(0)int xf(sinx)dx=Aoverset(pi//2)underset(0)intf(sinx)dx`
`=pioverset(pi//2)underset(0)intf(sin x)dx=Aoverset(pi//2)underset(0)int f(sin x)dx`
`rArr A=pi`
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OBJECTIVE RD SHARMA-DEFINITE INTEGRALS-Chapter Test 2
  1. If int(0)^(pi)xf(sinx)dx=A int(0)^(pi//2) f(sinx)dx, then A is

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  2. The integral int(0)^(r pi) sin^(2x)x dx is equal to

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  3. The value of the integral int(0)^(2)x[x]dx

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  4. The value of integral sum (k=1)^(n) int (0)^(1) f(k - 1+x) dx is

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  5. Let f(x) be a funntion satifying f'(x)=f(x) with f(0)=1 and g(x) be th...

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  6. If I=int(0)^(1) cos{ 2 "cot"^(-1)sqrt((1-x)/(1+x))}dx then

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  7. The value of int(a)^(a+(pi//2))(sin^(4)x+cos^(4)x)dx is

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  8. The vaue of int(-1)^(2) (|x|)/(x)dx is

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  9. The value of int0^1 (x^(3))/(1+x^(8))dx is

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  10. The value of int(0)^(3) xsqrt(1+x)dx, is

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  11. The value of the integral int(0)^(1) log sin ((pix)/(2))dx is

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  12. The value of the integral int(0)^(pi)x log sin x dx is

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  13. If I(1)=int(0)^(oo) (dx)/(1+x^(4))dx and I(2)underset(0)overset(oo)in...

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  14. If f(x)={{:(x,"for " x lt 1),(x-1,"for " x ge1):},"then" int(0)^(2) x...

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  15. The value of the integral int(0)^(2) (1)/((x^(2)+1)^(3//2))dx is

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  16. If int(0)^(2a) f(x)dx=int(0)^(2a) f(x)dx, then

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  17. If int(0)^(36) (1)/(2x+9)dx =log k, is equal to

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  18. The value of the integral int(0)^(pi//2) sin^(6) x dx, is

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  19. If int(0)^(oo) e^(-x^(2))dx=sqrt((pi)/(2))"then"int(0)^(oo) e^(-ax^(2)...

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  20. The value of the integral int 0^oo 1/(1+x^4)dx is

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  21. If int(pi//2)^(x) sqrt(3-2sin^(2)u) dx+int(dx)^(dy) equal pi//2

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