The sum of 5x^2 + x and -2x^2 - 3x - 1 ?

5x^2 + x -2x^2 -3x -1 =

Add (algebraically) the common terms; i.e.,
5x^2-2x^2 = 3x^2
x-3x = -2x and the answer is
3x^2 - 2x - 1.