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).

A trapezoid is a quadrilateral with one set of parallel sides.

Perimeter is equal to the sum of the four sides:

p = a + b + c + d
p = 1 + 5 + 8 + 6
p = 20

To combine like terms, add or subtract the coefficients (the numbers that come before the variables) of terms that have the same variable raised to the same exponent.

9a + 6a = 15a

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.

9c + 4 < \( \frac{c}{8} \)
8 x (9c + 4) < c
(8 x 9c) + (8 x 4) < c
72c + 32 < c
72c + 32 - c < 0
72c - c < -32
71c < -32
c < \( \frac{-32}{71} \)
c < -\(\frac{32}{71}\)