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.

(5a)(9ab) - (5a²)(5b)
(5 x 9)(a x a x b) - (5 x 5)(a² x b)
(45)(a¹⁺¹ x b) - (25)(a²b)
45a²b - 25a²b
20a²b

The circumference of a circle is the distance around its perimeter and equals π (approx. 3.14159) x diameter: c = π d. The area of a circle is π x (radius)² : a = π r².

A circle is a figure in which each point around its perimeter is an equal distance from the center. The radius of a circle is the distance between the center and any point along its perimeter. A chord is a line segment that connects any two points along its perimeter. The diameter of a circle is the length of a chord that passes through the center of the circle and equals twice the circle's radius (2r).

The first step to solve a quadratic equation that's set to zero is to factor the quadratic equation:

x² + x - 72 = 0
(x - 8)(x + 9) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (x - 8) or (x + 9) must equal zero:

If (x - 8) = 0, x must equal 8
If (x + 9) = 0, x must equal -9

So the solution is that x = 8 or -9

The entire length of this line is represented by AD which is AB + BD:

AD = AB + BD