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).

To solve this equation, isolate the variable for which you are solving (a) on one side of the equation and put everything else on the other side.

-a + 2z = -2a + 9z + 2
-a = -2a + 9z + 2 - 2z
-a + 2a = 9z + 2 - 2z
a = 7z + 2

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:

(y + 5)(y + 7)
(y x y) + (y x 7) + (5 x y) + (5 x 7)
y² + 7y + 5y + 35
y² + 12y + 35

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 x 7b = (5 x 7) (a x b) = 35ab

The formula for area is πr²:

a = πr²
a = π(5²)
a = 25π