A triangle is a three-sided polygon. It has three interior angles that add up to 180° (a + b + c = 180°). An exterior angle of a triangle is equal to the sum of the two interior angles that are opposite (d = b + c). The perimeter of a triangle is equal to the sum of the lengths of its three sides, the height of a triangle is equal to the length from the base to the opposite vertex (angle) and the area equals one-half triangle base x height: a = ½ base x height.

The Pythagorean theorem defines the relationship between the side lengths of a right triangle. The length of the hypotenuse squared (c²) is equal to the sum of the two perpendicular sides squared (a² + b²): c² = a² + b² or, solved for c, \(c = \sqrt{a + b}\)

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

a = l x w
a = a x b
a = 3 x 9
a = 27

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.

(3a)(9ab) + (6a²)(3b)
(3 x 9)(a x a x b) + (6 x 3)(a² x b)
(27)(a¹⁺¹ x b) + (18)(a²b)
27a²b + 18a²b
45a²b

A rhombus is a parallelogram with four equal-length sides. A square is a rectangle with four equal-length sides.