设α,β为钝角sinα=x,cosβ=y,cos(α+β)=5/13,且y=f(x)则f(x)的表达式

Question

设α,β为钝角sinα=x,cosβ=y,cos(α+β)=5/13,且y=f(x)则f(x)的表达式

Answer 1

cos(α+β)=5/13,sin(α+β)= -12/13
cosαcosβ-sinαsinβ=5/13
-√(1-x^2)*y-x*sinβ=5/13
sinαcosβ+cosαsinβ= -12/13
x*y-√(1-x^2)sinβ=-12/13
-√(1-x^2)*y-x*(x*y+12/13)/√(1-x^2)=5/13
y=-12/13-5/13*√(1-x^2)