bagaimana cara Nomor 5 beserta Caranya . ini penting banget . makasih

trigonometri
(1 + tan² x) (1- cos² x) = tan² x
ruas kiri
(1 + tan² x) (1 - cos² x)
= {(1 + sin² x/(cos² x)} (sin² x)
= {(cos² x + sin² x)/cos² x)}  (sin² x)
= (1/cos² x) (sin² x)
= (sin² x/cos² x)
= (sin x/cos x)²
= (tan x )²
= tan² x