三角函数.sinπ/10cos兀/5
问题描述：
三角函数.sinπ/10cos兀/5
答
原式=2sin(π/10)cos(π/10)cos(π/5)/2cos(π/10)
=sin(π/5)cos(π/5)/2cos(π/10)
=2sin(π/5)cos(π/5)/4cos(π/10)
=sin(2π/5)/4cos(π/10)
=cos(π/2-2π/5)/4cos(π/10)
=cos(π/10)/4cos(π/10)
=1/4想到了但没解出来。