Question

若(π/3-2x)的余弦值等于-7/8,则(x+π/3)的正弦值等于多少

Answer 1

‍cos‍(π/3-2x)=-7/8

所以cos[π-(π/3-2x)]=cos2(x+π/3)=7/8

所以cos2(x+π/3)

=cos2(x+π/3)

=2[cos(x+π/3)]^2-1

=7/8

所以cos(x+π/3)=±√15/4‍

所以sin‍(x+π/3)=±1/4‍