Question

三角函数化简题：1+sin(a-2派）*sin(派+a)—2cos^2(-a)=

Answer 1

1+sin(a-2派）*sin(派+a)—2cos^2(-a)
=1-sin(2派-a）*sin(派+a)—2cos^2(-a)
=1+sin(-a）*sin(a)—2cos^2(a)
=sin(-a）*sin(a)—(2cos^2(a)-1)
=-sinasina-cos2a
=-sin^2a-(1-2sin^2a)
=sin^2a-1
=-cos^2a。