(sin3x+sinx)/(cos3x+cosx)=

问题描述:

(sin3x+sinx)/(cos3x+cosx)=

(sin3x+sinx)/(cos3x+cosx)
=2sin2xcosx/(2cos2xcosx)
=tan2x

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