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 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 -42 as well and sum (Inside, Outside) to equal 1. For this problem, those two numbers are -6 and 7. Then, plug these into a set of binomials using the square root of the First variable (y²):

y² + y - 42
y² + (-6 + 7)y + (-6 x 7)
(y - 6)(y + 7)

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.

5a⁹ - 6a⁹ = -1a⁹

The volume of a cube is height x length x width:

v = h x l x w
v = 3 x 1 x 3
v = 9

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.