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 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.

3a⁷ - 4a⁷ = -1a⁷

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 + 4)(y - 8)
(y x y) + (y x -8) + (4 x y) + (4 x -8)
y² - 8y + 4y - 32
y² - 4y - 32

To factor a quadratic expression, apply the FOIL method (First, Outside, Inside, Last) in reverse. First, find the two Last terms that will multiply to produce -16 as well and sum (Inside, Outside) to equal 6. For this problem, those two numbers are -2 and 8. Then, plug these into a set of binomials using the square root of the First variable (y²):

y² + 6y - 16
y² + (-2 + 8)y + (-2 x 8)
(y - 2)(y + 8)

A parallelogram is a quadrilateral with two sets of parallel sides. Opposite sides (a = c, b = d) and angles (red = red, blue = blue) are equal. The area of a parallelogram is base x height and the perimeter is the sum of the lengths of all sides (a + b + c + d).