Perimeter is equal to the sum of the four sides:

p = a + b + c + d
p = 9 + 8 + 1 + 2
p = 20

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.

A monomial contains one term, a binomial contains two terms, and a polynomial contains more than two terms.

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 -18 as well and sum (Inside, Outside) to equal 7. For this problem, those two numbers are -2 and 9. Then, plug these into a set of binomials using the square root of the First variable (y²):

y² + 7y - 18
y² + (-2 + 9)y + (-2 x 9)
(y - 2)(y + 9)

For parallel lines with a transversal, the following relationships apply:

• angles in the same position on different parallel lines equal each other (a° = w°, b° = x°, c° = z°, d° = y°)
• alternate interior angles are equal (a° = z°, b° = y°, c° = w°, d° = x°)
• all acute angles (a° = c° = w° = z°) and all obtuse angles (b° = d° = x° = y°) equal each other
• same-side interior angles are supplementary and add up to 180° (e.g. a° + d° = 180°, d° + c° = 180°)

Applying these relationships starting with w° = 20, the value of c° is 20.