sin(β-α)=√10/10, α,β为锐角, cos(β-α)=√{1-[sin(β-α)]^2}=3/√10, sinα=√5/5, cosα=2/√5, sinβ=sin(β-α+α) =sin(β-α)*cosα+cos(β-α)*sinα =√2/2. β=45度.
