A right angle measures 90 degrees and is the intersection of two perpendicular lines. In diagrams, a right angle is indicated by a small box completing a square with the perpendicular lines.

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) - (5a²)(2b)
(3 x 9)(a x a x b) - (5 x 2)(a² x b)
(27)(a¹⁺¹ x b) - (10)(a²b)
27a²b - 10a²b
17a²b

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 perimeter of a triangle is the sum of the lengths of its sides:

p = x + y + z
p = 7cm + 15cm + 6cm = 28cm

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