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.

The volume of a cube is height x length x width:

v = h x l x w
v = 5 x 5 x 9
v = 225

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

a = l x w
a = a x b
a = 8 x 9
a = 72

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.

-b + 7 < \( \frac{b}{6} \)
6 x (-b + 7) < b
(6 x -b) + (6 x 7) < b
-6b + 42 < b
-6b + 42 - b < 0
-6b - b < -42
-7b < -42
b < \( \frac{-42}{-7} \)
b < 6

The circumference of a circle is the distance around its perimeter and equals π (approx. 3.14159) x diameter: c = π d. The area of a circle is π x (radius)² : a = π r².