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

a = l x w
a = a x b
a = 3 x 1
a = 3

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.

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.

(4a)(5ab) - (2a²)(6b)
(4 x 5)(a x a x b) - (2 x 6)(a² x b)
(20)(a¹⁺¹ x b) - (12)(a²b)
20a²b - 12a²b
8a²b

The surface area of a cylinder is 2πr² + 2πrh:

sa = 2πr² + 2πrh
sa = 2π(3²) + 2π(3 x 1)
sa = 2π(9) + 2π(3)
sa = (2 x 9)π + (2 x 3)π
sa = 18π + 6π
sa = 24π

To multiply binomials, use the FOIL method. FOIL stands for First, Outside, Inside, Last and refers to the position of each term in the parentheses.