(sinα+cosα)²=9/5
2sinacosa=4/5
1-2sinacosa=1-4/5=1/5
(sina-cosa)²=(√5/5)²
sina-cosa=±√5/5
sina=2√5/5,cosa=-√5/5
sina=-√5/5,cosa=2√5/5
tanα=-2或-1/2