|a|=|b|
=>(sinα)^2+(cosα-2sinα)^2 = 5
5(sinα)^2 -4sinαcosα + (cosα)^2 =5
4(cosα)^2 + 4sinαcosα =0
cosα(cosα+sinα) =0
=> cosα+sinα =0
tanα= -1
α= 3π/45(sinα)^2 -4sinαcosα + (cosα)^2 =54(cosα)^2 + 4sinαcosα =0这两步变化错了吧应该是4(sinα)^2 + 4sinαcosα =4吧5(sinα)^2 -4sinαcosα + (cosα)^2 =5-4sinαcosα + (cosα)^2 = 5- 5(sinα)^2 = 5(cosα)^24(cosα)^2 + 4sinαcosα =0