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).

The area of a trapezoid is one-half the sum of the lengths of the parallel sides multiplied by the height:

a = ½(b + d)(h)
a = ½(3 + 7)(3)
a = ½(10)(3)
a = ½(30) = \( \frac{30}{2} \)
a = 15

To multiply monomials, multiply the coefficients (the numbers that come before the variables) of each term, add the exponents of like variables, and multiply the different variables together.

(7a)(6ab) - (2a²)(6b)
(7 x 6)(a x a x b) - (2 x 6)(a² x b)
(42)(a¹⁺¹ x b) - (12)(a²b)
42a²b - 12a²b
30a²b

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.

The formula for area is πr²:

a = πr²
a = π(4²)
a = 16π