An equation is two expressions separated by an equal sign. The key to solving equations is to repeatedly do the same thing to both sides of the equation until the variable is isolated on one side of the equal sign and the answer on the other.

Perimeter is equal to the sum of the four sides:

p = a + b + c + d
p = 1 + 5 + 2 + 7
p = 15

To multiply binomials, use the FOIL method. FOIL stands for First, Outside, Inside, Last and refers to the position of each term in the parentheses:

(y - 2)(y - 9)
(y x y) + (y x -9) + (-2 x y) + (-2 x -9)
y² - 9y - 2y + 18
y² - 11y + 18

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.

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 equal sign and the answer on the other.

9b + 5 = \( \frac{b}{1} \)
1 x (9b + 5) = b
(1 x 9b) + (1 x 5) = b
9b + 5 = b
9b + 5 - b = 0
9b - b = -5
8b = -5
b = \( \frac{-5}{8} \)
b = -\(\frac{5}{8}\)