A triangle is a three-sided polygon. It has three interior angles that add up to 180° (a + b + c = 180°). An exterior angle of a triangle is equal to the sum of the two interior angles that are opposite (d = b + c). The perimeter of a triangle is equal to the sum of the lengths of its three sides, the height of a triangle is equal to the length from the base to the opposite vertex (angle) and the area equals one-half triangle base x height: a = ½ base x height.

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 - 4)
(y x y) + (y x -4) + (2 x y) + (2 x -4)
y² - 4y + 2y - 8
y² - 2y - 8

The area of a triangle is equal to ½ base x height:

a = ½bh
a = ½ x 6 x 3 = \( \frac{18}{2} \) = 9

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 - 4a = 5a

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