设x为锐角,若cos(x+30°)=4/5 ,sin(2x+15°)等于?

设x为锐角,若cos(x+30°)=4/5 ,sin(2x+15°)等于?
设x为锐角,若cos(x+30°)=4/5 ,sin(2x+15°)等于?

设x为锐角,若cos(x+30°)=4/5 ,sin(2x+15°)等于?
解决方案,cosxcos30°-sinxsin30°+的sinx = 0/5
√3/2cosx 1 / 2sinx = 0/5
COS（X-30°）= 8/10
COS（X-60°）= COS2（X-30°）= 2cos ^ 2（X-60°）-1 = 2 *（4/5）^ 2 = 7/25