log2cosπ/5+log2cos2π/5=

问题描述:

log2cosπ/5+log2cos2π/5=
要过程

log2cosπ/5+log2cos2π/5=log2(cosπ/5*cos2π/5)=log2[(2sinπ/5*cosπ/5*cos2π/5)/2sinπ/5]=log2[(sin2π/5*cos2π/5)/2sinπ/5]=log2[(sin4π/5)/2*2sinπ/5]=log2(1/4)=-2