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.

(7a)(3ab) - (7a²)(5b)
(7 x 3)(a x a x b) - (7 x 5)(a² x b)
(21)(a¹⁺¹ x b) - (35)(a²b)
21a²b - 35a²b
-14a²b

To solve this equation, replace the variables with the values given and then solve the now variable-free equation. (Remember order of operations, PEMDAS, Parentheses, Exponents, Multiplication/Division, Addition/Subtraction.)

-5b(b - z)
-5(-2)(-2 - 7)
-5(-2)(-9)
(10)(-9)
-90

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 formula for area is πr²:

a = πr²
a = π(3²)
a = 9π

According to the Pythagorean theorem, the hypotenuse squared is equal to the sum of the two perpendicular sides squared:

c² = a² + b²
c² = 8² + 9²
c² = 64 + 81
c² = 145
c = \( \sqrt{145} \)