Question 998842
(2x + 5)^2 − (x − 4)^2 
compute the squares
4x^2 +20x +25 - (x^2 -8x +16)
now distribute - sign
4x^2 +20x +25 -x^2 +8x -16
combine terms
3x^2 +28x +9
factor polynomial
(3x+1) * (x+9)