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.

A monomial contains one term, a binomial contains two terms, and a polynomial contains more than two terms.

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.

6a x 8b = (6 x 8) (a x b) = 48ab

The first step to solve a quadratic expression that's not set to zero is to solve the equation so that it is set to zero:

b² + 6b - 21 = -b - 3
b² + 6b - 21 + 3 = -b
b² + 6b + b - 18 = 0
b² + 7b - 18 = 0

Next, factor the quadratic equation:

b² + 7b - 18 = 0
(b - 2)(b + 9) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (b - 2) or (b + 9) must equal zero:

If (b - 2) = 0, b must equal 2
If (b + 9) = 0, b must equal -9

So the solution is that b = 2 or -9

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

a = l x w
a = a x b
a = 3 x 7
a = 21