若3SinX=CosX,则Cos2X+Sin2X等于?
问题描述：
若3SinX=CosX,则Cos2X+Sin2X等于?
答
sin^2x+cos^2x=1
sin^2x+9sin^2x=1
sin^2x=1/10
Cos2X+Sin2X
=cos^2x-sin^2x+2sinxcosx
=9sin^2x-sin^2x+6sin^2x
=14sin^2x
=7/5