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