一道函数计算

1/2-(cos3π/8)^2
=1/2-(1+cos3π/4)/2
=-(cos3π/4)/2
=√2/4.

公式:
(cosx)^2=(1+cos2x)/2

1/2-cos3n/8^2
=1/2-(1+cos3n/4)/2
=-(cos3n/4)/2
=……
应该会了吧

1/2-cos^2(3π/8)
=1/2-[1+cos(2*3π/8)]/2
={1-[1+cos(3π/4)]}/2
=[-cos(3π/4)]/2
=-cos(π-π/4)/2
=-[-cos(π/4)]/2
=cos(π/4)/2
=(根号2/2)/2
=根号2/4

1/2-(cos(四分之三派)+1)/2=跟号二/4