To factor a quadratic expression, apply the FOIL method (First, Outside, Inside, Last) in reverse. First, find the two Last terms that will multiply to produce -36 as well and sum (Inside, Outside) to equal -5. For this problem, those two numbers are -9 and 4. Then, plug these into a set of binomials using the square root of the First variable (y²):

y² - 5y - 36
y² + (-9 + 4)y + (-9 x 4)
(y - 9)(y + 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.

(8a)(7ab) + (3a²)(7b)
(8 x 7)(a x a x b) + (3 x 7)(a² x b)
(56)(a¹⁺¹ x b) + (21)(a²b)
56a²b + 21a²b
77a²b

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.

9a⁹ - 3a⁹ = 6a⁹

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.

9a x 2b = (9 x 2) (a x b) = 18ab

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.

5a + 8a = 13a