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 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.

3a⁹ - 3a⁹ = 0a⁹

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

b² - 6b + 5 = 0
(b - 1)(b - 5) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (b - 1) or (b - 5) must equal zero:

If (b - 1) = 0, b must equal 1
If (b - 5) = 0, b must equal 5

So the solution is that b = 1 or 5

To factor a quadratic expression, apply the FOIL method (First, Outside, Inside, Last) in reverse. First, find the two Last terms that will multiply to produce 9 as well and sum (Inside, Outside) to equal -10. For this problem, those two numbers are -9 and -1. Then, plug these into a set of binomials using the square root of the First variable (y²):

y² - 10y + 9
y² + (-9 - 1)y + (-9 x -1)
(y - 9)(y - 1)

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 - 3)(y + 2)
(y x y) + (y x 2) + (-3 x y) + (-3 x 2)
y² + 2y - 3y - 6
y² - y - 6