-6x^2 + 13x^2

-6x^2 + 13x^2 can be simplified by combining like terms:

-6x^2 + 13x^2 = 7x^2

To simplify the expression -6x^2 + 13x^2, we combine the like terms:

-6x^2 + 13x^2 = (13 - 6)x^2 = 7x^2

So, the simplified expression is 7x^2.