cos(π/4-x)cos(π/4+x)=根号2/6(

问题描述:

cos(π/4-x)cos(π/4+x)=根号2/6(

π/4-x+π/4+x=π/2 cos(π/4-x)cos(π/4+x)=sin(π/4+x)cos(π/4+x)==1/2sin(π/2+2x)
=1/2cos2x=√2/6 cos2x=√2/3 sin2x==√7/3