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.

The area of a parallelogram is equal to its length x width:

a = l x w
a = a x b
a = 8 x 3
a = 24

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 - 3a = 6a

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.

(2a)(9ab) + (8a²)(4b)
(2 x 9)(a x a x b) + (8 x 4)(a² x b)
(18)(a¹⁺¹ x b) + (32)(a²b)
18a²b + 32a²b
50a²b

A quadrilateral is a shape with four sides. The perimeter of a quadrilateral is the sum of the lengths of its four sides.