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 + 6a = 13a

To factor a quadratic expression, apply the FOIL (First, Outside, Inside, Last) method in reverse.

The Pythagorean theorem defines the relationship between the side lengths of a right triangle. The length of the hypotenuse squared (c²) is equal to the sum of the two perpendicular sides squared (a² + b²): c² = a² + b² or, solved for c, \(c = \sqrt{a + b}\)

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 -56 as well and sum (Inside, Outside) to equal -1. For this problem, those two numbers are -8 and 7. Then, plug these into a set of binomials using the square root of the First variable (y²):

y² - y - 56
y² + (-8 + 7)y + (-8 x 7)
(y - 8)(y + 7)

To multiply binomials, use the FOIL method. FOIL stands for First, Outside, Inside, Last and refers to the position of each term in the parentheses:

(y - 2)(y - 9)
(y x y) + (y x -9) + (-2 x y) + (-2 x -9)
y² - 9y - 2y + 18
y² - 11y + 18