若sinα=根号10/10,β=arc cos(-根号5/5),0<α<π/2,求证:α+β=3π/4快..=
问题描述:
若sinα=根号10/10,β=arc cos(-根号5/5),0<α<π/2,求证:α+β=3π/4
快..=
答
sinα=根号10/10,0<α<π/2,则cosα=3根号10/10
β=arc cos(-根号5/5),故β>π/2,sinβ=(-2根号5/5),cosβ=(-根号5/5),
由于sin(α+β)=sinαcosβ+sinβcosα=(根号2)/2,且0<α<π/2,β>π/2则
α+β=3π/4