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, \(c = \sqrt{a + b}\)

The surface area of a cube is (2 x length x width) + (2 x width x height) + (2 x length x height):

sa = 2lw + 2wh + 2lh
sa = (2 x 6 x 9) + (2 x 9 x 9) + (2 x 6 x 9)
sa = (108) + (162) + (108)
sa = 378

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 solve this equation, repeatedly do the same thing to both sides of the equation until the variable is isolated on one side of the equal sign and the answer on the other.

3x + 7 = 6 + 2x
3x = 6 + 2x - 7
3x - 2x = 6 - 7
x = -1

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 -4 as well and sum (Inside, Outside) to equal -3. For this problem, those two numbers are -4 and 1. Then, plug these into a set of binomials using the square root of the First variable (y²):

y² - 3y - 4
y² + (-4 + 1)y + (-4 x 1)
(y - 4)(y + 1)