V
vanmanh2001


Bài 1 . Rút gọn
$A = \cos ^3a \sin a - \sin ^3a \cos a$
$B = \dfrac{1+ \sin 2a - 2\sin ^2(\dfrac{\pi}{4} - a) }{4 \cos a}$
Bài 2
C/m $\sin ^6 a + \cos ^6 a = \dfrac{5+3\cos 4a}{8}$
$A = \cos ^3a \sin a - \sin ^3a \cos a$
$B = \dfrac{1+ \sin 2a - 2\sin ^2(\dfrac{\pi}{4} - a) }{4 \cos a}$
Bài 2
C/m $\sin ^6 a + \cos ^6 a = \dfrac{5+3\cos 4a}{8}$