A rhombus is a parallelogram with four equal-length sides. A square is a rectangle with four equal-length sides.

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

c² - 9c + 18 = 0
(c - 3)(c - 6) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (c - 3) or (c - 6) must equal zero:

If (c - 3) = 0, c must equal 3
If (c - 6) = 0, c must equal 6

So the solution is that c = 3 or 6

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.

The area of a rectangle is equal to its length x width:

a = l x w
a = a x b
a = 5 x 3
a = 15

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.