Question

sin(60-x)=1/4,cos(60+2x)=

Answer 1

sin(60-x)=1/4

则cos[90°-(60°-x)]=sin(60-x)=1/4

cos(30°+x)=1/4

cos(60°+2x)=cos2(30°+x)

=2cos²(30°+x)-1

=2*(1/4)²-1

=-7/8

即-8分之7