(sin3x+sinx)/(cos3x+cosx)=
网友回答
sinα+sinβ=2sin[(α+β)/2]cos[(α-β)/2]
cosα+cosβ=2cos[(α+β)/2]cos[(α-β)/2]
所以：(sin3x+sinx)/(cos3x+cosx)
=2sin2xcosx/(2cos2xcosx)
=sin2x/cos2x
=tam2x
======以下答案可供参考======
供参考答案1:
(sin3x+sinx)/(cos3x+cosx)
=2sin2xcosx/(2cos2xcosx)
=tan2x