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 72 as well and sum (Inside, Outside) to equal -17. For this problem, those two numbers are -9 and -8. Then, plug these into a set of binomials using the square root of the First variable (y²):

y² - 17y + 72
y² + (-9 - 8)y + (-9 x -8)
(y - 9)(y - 8)

Angles around a line add up to 180°. Angles around a point add up to 360°. When two lines intersect, adjacent angles are supplementary (they add up to 180°) and angles across from either other are vertical (they're equal).

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 + 7a = 12a

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 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.

(3a)(9ab) - (7a²)(5b)
(3 x 9)(a x a x b) - (7 x 5)(a² x b)
(27)(a¹⁺¹ x b) - (35)(a²b)
27a²b - 35a²b
-8a²b