tana=3,则sin平方a-cos平方a=详细过程谢谢..

网友回答

sin平方a-cos平方a
=(sin平方a-cos平方a)/(sin平方a+cos平方a)
=(tan平方a-1)/(tan平方a+1)
=(9-1)/(9+1)
=4/5======以下答案可供参考======
供参考答案1:
(sinα)^2 - (cosα)^2
=(cosα * tanα)^2 - (cosα)^2
=(cosα)^2 * [(tanα)^2 - 1]
= 1/(secα)^2 * [(tanα)^2 -1]
= [(tanα)^2 -1]/[(tanα)^2 + 1] 注：secα = 1/cosα，(secα)^2 = 1+(tanα)^2
= [3^2 -1]/[3^2 + 1]
=8/10 = 4/5