Question of the Day By Maths Grinds

With the help of Rolle’s Theorem and the function $f\left(x\right)=e^{-x} \left(x-a\right)\left(x-b\right)$ prove that the equation $\left(x-a\right)\left(x-b\right)=\left(x-a\right)+\left(x-b\right)$ will have a solution in the set $\left(a,b\right)$ where $a < b$.