cos(2x+60`)cos(x-30`)+sin(2x+60`)sin(x-30`)=1/2

问题描述:

cos(2x+60`)cos(x-30`)+sin(2x+60`)sin(x-30`)=1/2
求这题的题解...
60` 是60度.

原式=
cos[(2x+60)-(x-30)]=1/2
cos(x+90)=1/2
x+90=±30+2k∏