∵α,β均为锐角且sinα＝√5/5∴cosα＝√(1－sin²α)＝2√5/5cos(α－β)＝√[1－sin²(α－β)]＝3√10/10∴sinβ＝sin[α－(α－β)]＝sinαcos(α－β)－cosαsin(α－β)＝(√5/5)•(3√10/10)...