Bagaimana cara mencari identitas trigonometri soal no. 3 tlng dibantu

(1 + tan^2 ) * ( 1- cos^2) = tan^2

1 + tan^2 - cos^2 - tan^2 * cos^2 = tan^2
tan^2 + (1 - cos^2) - sin^2/cos^2 * cos^2 = tan^2
tan^2 + sin^2 - sin^2 = tan^2
tan^2 = tan^2

Terbukti

Identitas yang di gunakan :
-cos^2 + sin^2 = 1
-tan = sin/cos

Distributif
1-cos²x+tan²x- tan²x cos²x = tan²x
1-cos²x+tan²x-(sin²x/cos²x)cos²x = tan²x
(cos²x+sin²x)-cos²x+tan²x-sin²x = tan²x
(cos²x-cos²x)+(sin²x-sin²x)+tan²x = tan²x
tan²x = tan²x... Terbukti