sin18度+2*（sin18度)^2

热心网友

sin2A=2sinAcosA---cosA=sin2A/(2sinA)sin18+2(sin18)^2=sin18+(1-cos36)=1+sin18-sin54=1+2cos36sin(-18)=1-2cos36cos72=1-2*sin72/(2sin36)*sin144/(2sin72)=1-in144/(2sin36)=1-sin36/(2sin36)=1-1/2=1/2