A right angle measures 90 degrees and is the intersection of two perpendicular lines. In diagrams, a right angle is indicated by a small box completing a square with the perpendicular lines.

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 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.

(9a)(3ab) + (3a²)(9b)
(9 x 3)(a x a x b) + (3 x 9)(a² x b)
(27)(a¹⁺¹ x b) + (27)(a²b)
27a²b + 27a²b
54a²b

To solve this equation, repeatedly do the same thing to both sides of the equation until the variable is isolated on one side of the > sign and the answer on the other.

-5y + 4 > \( \frac{y}{5} \)
5 x (-5y + 4) > y
(5 x -5y) + (5 x 4) > y
-25y + 20 > y
-25y + 20 - y > 0
-25y - y > -20
-26y > -20
y > \( \frac{-20}{-26} \)
y > \(\frac{10}{13}\)

Perimeter is equal to the sum of the four sides:

p = a + b + c + d
p = 4 + 7 + 3 + 4
p = 18