呢題乘數點計牙?????????急!!!!!!聽日交牙!!!

首先，你要知道以下呢個定理
sin(A+B)
= sinAcosB + cosAsinB

所以
當A = 12，B = 78時
sin12 cos78 + sin78 cos12
= sin (12+78)
= sin90
= 1//

cos 78 = cos (90 - 12) = sin 12
sin 78 = sin (90 - 12) = cos 12
Therefore, sin 12 cos 78 + sin 78 cos 12
= sin^2 12 + cos^2 12
= 1

sin 12˚ cos 78˚ + sin 78˚ cos 12˚
=sin(12˚+78˚)
=sin90˚
=1