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The function f(x) = sin ^(4)x+ cos ^(4)x...

The function `f(x) = sin ^(4)x+ cos ^(4)x ` increases, if

A

`0ltxltpi//8`

B

`pi//40ltxlt3pi//8`

C

`3pi//8ltxlt5pi//8`

D

`5pi//8ltxlt3pi//4`

Text Solution

Verified by Experts

The correct Answer is:
2
We have f(x) = `sin^(4)x + cos^(4)x=3/4+1/4cosx`
`therefore f(X)=-sin 4x`
Now `f(X) gt0 or - sin 4xgt0`
or `sin4xlt0 or pilt4xlt2pi`
or `pi//4 ltxltpi//2`
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