cos^2(π/3-a)+cos^2(π/6+a)
=cos^2(π/3-a)+sin^2(π/3-a)
=1为什么cos^2(π/6+a)=sin^2(π/3-a)啊小弟我没学过╮(╯_╰)╭（π/6+a）+（π/3-a）=π/2两角互余。若A+B=π/2，则cosA=sinB