When solving an equation with two variables, replace the variables with the values given and then solve the now variable-free equation. (Remember order of operations, PEMDAS, Parentheses, Exponents, Multiplication/Division, Addition/Subtraction.)

The coordinate grid is composed of a horizontal x-axis and a vertical y-axis. The center of the grid, where the x-axis and y-axis meet, is called the origin.

The first step to solve a quadratic equation that's set to zero is to factor the quadratic equation:

x² - 4x - 12 = 0
(x + 2)(x - 6) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (x + 2) or (x - 6) must equal zero:

If (x + 2) = 0, x must equal -2
If (x - 6) = 0, x must equal 6

So the solution is that x = -2 or 6

The volume of a cylinder is πr²h:

v = πr²h
v = π(1² x 9)
v = 9π

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).