已知sinα=2sinβ,tanα=3tanβ,α是锐角,求cosα的值
问题描述:
已知sinα=2sinβ,tanα=3tanβ,α是锐角,求cosα的值
答
sinα=2sinβ (1)
tanα=3tanβ
sinα/ cosα = 3tanβ (2)
(2)/(1)
cosα = 3tanβ/2sinβ
= 3/(2cosβ)