Lim x mendekati 0 cos x-cos 3x/1-cos 2x =

jawab

cos A - cos B = -2 sin 1/2 (A +B) sin 1/2 (A - B)
1 - cos 2x = 1 - (1 - 2 sin² x) = 2 sin² x

limit x→ 0  (cos x  - cos 3x ) /( 1- cos 2x)=

limit x→ 0 (- 2 sin1/2 (x + 3x) sin 1/2 (x-3x) /(2 sin² x)

limit x→0 (- 2 sin 2x sin (-x) ) / 2 sin² x)
= (-2)(2)(-1)/(2)(1)²
= 4/2
= 2