y=sin²X+2sinXcosX-3cos²X
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y=sin²X+2sinXcosX-3cos²Xy=sin²X+2sinXcosX-3cos²Xy=sin²X+2sinXcosX-3cos²
y=sin²X+2sinXcosX-3cos²X
y=sin²X+2sinXcosX-3cos²X
y=sin²X+2sinXcosX-3cos²X
y=sin²x+2sinxcosx－3cos²x
=(sin²x+cos²x)+2sinxcosx－4cos²x
=1+2sinxcosx－4cos²x
=1+sin(2x)－2［cos(2x)＋1］
＝sin2x-2cos2x-1
如果是：y=sin²x+2sinxcosx+3cos²x
=(sin²x+cos²x)+2sinxcosx+2cos²x
=1+2sinxcosx+2cos²x
=1+sin(2x)+1+cos(2x)
=(√2)[(√2/2)sin(2x)+(√2/2)cos(2x)]+2
=(√2)[cos(π/4)sin(2x)+sin(π/4)cos(2x)]+2
=(√2)sin(2x+π/4)+2