Perimeter is equal to the sum of the four sides:

p = a + b + c + d
p = 3 + 9 + 2 + 4
p = 18

A circle is a figure in which each point around its perimeter is an equal distance from the center. The radius of a circle is the distance between the center and any point along its perimeter. A chord is a line segment that connects any two points along its perimeter. The diameter of a circle is the length of a chord that passes through the center of the circle and equals twice the circle's radius (2r).

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 5. For this problem, those two numbers are 1 and 4. Then, plug these into a set of binomials using the square root of the First variable (y²):

y² + 5y + 4
y² + (1 + 4)y + (1 x 4)
(y + 1)(y + 4)

To multiply monomials, multiply the coefficients (the numbers that come before the variables) of each term, add the exponents of like variables, and multiply the different variables together.

(7a)(5ab) + (3a²)(6b)
(7 x 5)(a x a x b) + (3 x 6)(a² x b)
(35)(a¹⁺¹ x b) + (18)(a²b)
35a²b + 18a²b
53a²b

Parallel lines are lines that share the same slope (steepness) and therefore never intersect. A transversal occurs when a set of parallel lines are crossed by another line. All of the angles formed by a transversal are called interior angles and angles in the same position on different parallel lines equal each other (a° = w°, b° = x°, c° = z°, d° = y°) and are called corresponding angles. Alternate interior angles are equal (a° = z°, b° = y°, c° = w°, d° = x°) and 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°).