1. (2023春•台江区校级期末)已知α\alphaα,β\betaβ都是锐角,sinα=35,cos(α+β)=−513\sin \alpha =\frac{3}{5},\cos (\alpha +\beta )=-\frac{5}{13}sinα=53,cos(α+β)=−135,则cosβ=(\cos \beta =(cosβ=( )))