sin平方（A-30度）＋sin平方(A+30度) - 知识问答

sin平方（A-30度）＋sin平方(A+30度)-sin平方A,化简

2个回答

sin^2(a+30)+sin^2(a-30)-sin^2a
=sin^2(a+30)+2sinasin30+sin^2(a-30)-2sinasin30-sin^2a
=[sin(a+30)+sin(a-30)]^2-sina-sin^2a
=[sinacos30+cosasin30+sinacos30-cosasin30]^2-sina-sin^2a
=[2sinacos30]^2-sina-sin^2a
=3sin^2a-sina-sin^2a
=2sin^2a-sina

相关问题