The integral function is

Rewrite the integral function is

Let .

Apply derivative on each side with respect to .

Substitutes and in  integral function.

Let

Apply derivative on each side with respect to .

Substitutes and  in  integral function.

Trigonometric property : .

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Double angle formula :

Consider .

For a right triangle, and 

then .

then .

Substitute corresponding values in the equation .

Substitute and in  integral function.

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