[tex]\lim_{x \to \ y} \frac{cos 2x - cos 2y}{ x-y} }[/tex] Dijawab yaa terimkasih~

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

Lim (cos 2x - cos 2y)/(x - y)
= Lim (-2 sin 1/2 (2x + 2y) sin 1/2 (2x - 2y)) / (x - y)
= Lim (-2 sin (x + y)) . (sin (x - y))/(x - y)
= -2 sin (y + y) . 1
= -2 sin 2y