To combine like terms, add or subtract the coefficients (the numbers that come before the variables) of terms that have the same variable raised to the same exponent.

7a + 2a = 9a

The first step to solve a quadratic equation that's set to zero is to factor the quadratic equation:

a² + 8a + 16 = 0
(a + 4)(a + 4) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, (a + 4) must equal zero:

If (a + 4) = 0, a must equal -4

So the solution is that a = -4

To multiply monomials, multiply the coefficients (the numbers that come before the variables) of each term, add the exponents of like variables, and multiply the different variables together.

(2a)(2ab) - (3a²)(7b)
(2 x 2)(a x a x b) - (3 x 7)(a² x b)
(4)(a¹⁺¹ x b) - (21)(a²b)
4a²b - 21a²b
-17a²b

To combine like terms, add or subtract the coefficients (the numbers that come before the variables) of terms that have the same variable raised to the same exponent.

9a² - 5a² = 4a²

When solving an equation with two variables, replace the variables with the values given and then solve the now variable-free equation. (Remember order of operations, PEMDAS, Parentheses, Exponents, Multiplication/Division, Addition/Subtraction.)