Hi there. Like terms are terms that have the same variable factors. 2x and 2y are not like terms, but 5x and -8x are like terms. x2 and x are NOT like terms, because x2=x*x (it has two variable factors). In an expression, find the like terms and add their coefficients to combine like terms.
-7x2 + 2x
Don't add exponents. Remember that x*x = x2 but 2x = x + x.