sin^2(a-30°)+sin^2(a+30°)-sin^2a=(sinacos30°-cosasin30°)^2+(sinacos30°+cosasin30°)^2-sin^2a=(√3/2*sina-1/2*cosa)^2+(√3/2*sina+1/2*cosa)^2-sin^2a=3/2*sin^2a+1/2*cos^2-sin^2a=1/2*sin^2a+1/2*cos^...