tolong bantu jawab beserta cara penyelesaiannya ya :) (nomor 10)

Jawaban B 
Pakai rumus f(x) = u/v
f'(x) = u'v-uv'/v²
u = sin x
u' = cos x
v = sin x + cos x
v' = cos x - sin x
v² = (sin x + cos x)²

f'(x) = cos x (sin x + cos x) - sin x (cos x - sin x) / (sin x + cos x)²
= cos x sin x + cos² x - sin x cos x + sin² x / (sin x + cos x)²
= cos² x + sin² x / (sin x + cos x)²
= 1 / (sin x + cos x)²