m与n为共线向量
=>(cosα-√2/3)/(-1)=sinα/1
-cosα+√2/3 = sinα
√2/3 = (sinα+cosα)
2/9 = 1+ sin2α
sin2α = -7/9
tan2α = -7/(4√2)
-cosα+√2/3 = sinα
√2/3 = (sinα+cosα) .(sinα-cosα)/(sinα-cosα)
= -cos2α/(sinα-cosα)
sin2α/(sinα-cosα) =-(√2/3)tan2α = (√2/3)(7/4√2) =7/12