sinx-cosx=1/2 平方
(sinx)^2+(cosx)^2-2sinxcosx=1/4
1-2sinxcosx=1/4
2sinxcosx=3/4
sin2x=3/4
(sinx+cosx)^2=(sinx-cosx)^2+4sinxcosx
(sinx+cosx)^2=(1/2)^2+2*3/4
(sinx+cosx)^2=1/4+6/4
(sinx+cosx)^2=7/4
sinx+cosx=±√7/2
sin2x-cos2x
=sin2x-[(cosx)^2-(sinx)^2]
=sin2x-(cosx)^2+(sinx)^2
=sin2x+(sinx)^2-(cosx)^2
=sin2x+(sinx-cosx)(sinx+cosx)
=3/4±√7/2*1/2
=3/4±√7/4