tolong dibantu berserta pembahasannya, terima kasih :)

IDENTITAS TRIGONOMETRI : 1 + tan^2 x = sec^2 x

1 - tan^2 4x + tan^4 4x - tan^6 4x + ... = S~
a = 1 dan r = (-tan^2 4x)/1 = - tan^2 4x
S~ = a/(1 - r) = 1/(1 - (-tan^2 4x)) = 1/(1 + tan^2 4x) = 1/(sec^2 4x) = cos^2 4x

Int √(1 - tan^2 4x + tan^4 4x - tan^6 4x + .... ) dx
= Int √(cos^2 4x) dx
= Int (cos 4x) dx
= 1/4 sin 4x + C