Question

已知cos2α/sin（α-45°）=cos120° 求sinα＋cosα=

Answer 1

[(cosα)^2-(sinα)^2]/[(√2sinα)/2-(√2cosα)/2]=-1/2,

√2[cosα+sinα)(cosα-sinα)/（sinα-cosα）=-1/2,

sinα+cosα=√2/4.