定义运算:x*y=x^2-y^2+2xy则cosπ/3*sinπ/3的值是为什么(cosπ/3)^2-(sinπ/3)^2=cos_数学解答

定义运算:x*y=x^2-y^2+2xy则cosπ/3*sinπ/3的值是
为什么(cosπ/3)^2-(sinπ/3)^2=cos2π/3？

人气：108 ℃　时间：2020-04-18 19:59:34

解答

cosπ/3*sinπ/3
=(cosπ/3)^2-(sinπ/3)^2+2cosπ/3sinπ/3
=cos2π/3+sin2π/3
=(3^0.5-1)/2