A(a+b)3(a+b)^3(a+b)3BaCbD(a+b)Answer: (a+b)3(a+b)^3(a+b)3 Read Explanation: $y=(a+b)$$y^2=(a+b)^2$3rd proportion =$ \frac{a}{b}=\frac{b}{c}$$\frac{y}{y^2}=\frac{y^2}{x}$$\frac{1}{y}=\frac{y^2}{x}$$x=y^3$$x=(a+b)^3$ Read more in App