An equation is two expressions separated by an equal sign. The key to solving equations is to 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.

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

x² - 8x + 15 = 0
(x - 3)(x - 5) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (x - 3) or (x - 5) must equal zero:

If (x - 3) = 0, x must equal 3
If (x - 5) = 0, x must equal 5

So the solution is that x = 3 or 5

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.

An isosceles triangle has two sides of equal length. An equilateral triangle has three sides of equal length. In a right triangle, two sides meet at a right angle.

A line on the coordinate grid can be defined by a slope-intercept equation: y = mx + b. For a given value of x, the value of y can be determined given the slope (m) and y-intercept (b) of the line. The slope of a line is change in y over change in x, \({\Delta y \over \Delta x}\), and the y-intercept is the y-coordinate where the line crosses the vertical y-axis.