Perimeter is equal to the sum of the four sides:

p = a + b + c + d
p = 9 + 1 + 4 + 5
p = 19

The formula for area is πr²:

a = πr²
a = π(3²)
a = 9π

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.

2a⁹ + 9a⁹ = 11a⁹

A line on the coordinate grid can be defined by a slope-intercept equation: y = mx + b. For a given value of x, the value of y can be determined given the slope (m) and y-intercept (b) of the line. The slope of a line is change in y over change in x, \({\Delta y \over \Delta x}\), and the y-intercept is the y-coordinate where the line crosses the vertical y-axis.

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 + 3)(y + 7)
(y x y) + (y x 7) + (3 x y) + (3 x 7)
y² + 7y + 3y + 21
y² + 10y + 21