已知tan(a+β)=7,tana*tanβ=2/3则cos(a-β)=

问题描述:

已知tan(a+β)=7,tana*tanβ=2/3则cos(a-β)=

tan(a+β)=7(tana+tanβ)/(1-tanatanβ) = 73(tana+tanβ) = 73sin(a+β)/cosacosβ = 7cosacosβ= 3sin(a+β)/7= 3(7/5√2)/7= 3/(5√2) = 3√2/10 tanatanβ = 2/3sinasinβ/cosacosβ = 2/3sinasinβ = (2/3)cosa...