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.

9a + 9a = 18a

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.

(5a)(3ab) + (2a²)(6b)
(5 x 3)(a x a x b) + (2 x 6)(a² x b)
(15)(a¹⁺¹ x b) + (12)(a²b)
15a²b + 12a²b
27a²b

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.

4a⁴ + 5a⁴ = 9a⁴

To solve this equation, 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.)

-5b(b - x)
-5(5)(5 - 9)
-5(5)(-4)
(-25)(-4)
100

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

y² + 8y - 9 = 0
(y - 1)(y + 9) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (y - 1) or (y + 9) must equal zero:

If (y - 1) = 0, y must equal 1
If (y + 9) = 0, y must equal -9

So the solution is that y = 1 or -9