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.

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

-c + 2z = c + 9z - 9
-c = c + 9z - 9 - 2z
-c - c = 9z - 9 - 2z
-2c = 7z - 9
c = \( \frac{7z - 9}{-2} \)
c = \( \frac{7z}{-2} \) + \( \frac{-9}{-2} \)
c = -3\(\frac{1}{2}\)z + 4\(\frac{1}{2}\)

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.

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:

z² + 5z - 16 = z - 4
z² + 5z - 16 + 4 = z
z² + 5z - z - 12 = 0
z² + 4z - 12 = 0

Next, factor the quadratic equation:

z² + 4z - 12 = 0
(z - 2)(z + 6) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (z - 2) or (z + 6) must equal zero:

If (z - 2) = 0, z must equal 2
If (z + 6) = 0, z must equal -6

So the solution is that z = 2 or -6

To combine like terms, add or subtract the coefficients (the numbers that come before the variables) of terms that have the same variable raised to the same exponent.

7a + 9a = 16a