Can someone get this? Ive been trying and cant get it

Given :-

To Find :-

Answer :-

The roots of the function are 5 and -3 . In general we can write the Quadratic function with roots π and ∆ as ,

f(x) = ( x - π )(x-∆)

So on using this we have ,

f(x) = ( x -5)( x -(-3))

f(x) = (x-5)(x+3)

f(x) = x(x-5)+3(x-5)

f(x) = x² -5x +3x -15

f(x) = x² -2x -15

Hence the required answer is x² -2x -15.