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The value of a for which the function f(...

The value of `a` for which the function `f(x)=asinx+(1/3)sin3x` has an extremum at `x=pi/3` is (a) 1 (b) `-1` (c) 0 (d) 2

A

1

B

-1

C

0

D

2

Text Solution

Verified by Experts

The correct Answer is:
5
If f(x) has an extremum at x=` pi//3` then f(X) =0 at q x=`pi//3`
Now f(X) = `a sinx +(1)/(3)` sin 3x
`therefore` f(x)=a cos x + cos 3x
`f'(pi//3)`=0`
or a=2
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