The formula for area is πr²:

a = πr²
a = π(2²)
a = 4π

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 18 as well and sum (Inside, Outside) to equal 11. For this problem, those two numbers are 2 and 9. Then, plug these into a set of binomials using the square root of the First variable (y²):

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

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

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.

(8a)(7ab) + (5a²)(9b)
(8 x 7)(a x a x b) + (5 x 9)(a² x b)
(56)(a¹⁺¹ x b) + (45)(a²b)
56a²b + 45a²b
101a²b

An isosceles triangle has two sides of equal length. An equilateral triangle has three sides of equal length. In a right triangle, two sides meet at a right angle.