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

c² - 9c + 18 = 0
(c - 3)(c - 6) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (c - 3) or (c - 6) must equal zero:

If (c - 3) = 0, c must equal 3
If (c - 6) = 0, c must equal 6

So the solution is that c = 3 or 6

To solve this equation, repeatedly do the same thing to both sides of the equation until the variable is isolated on one side of the equal sign and the answer on the other.

7y + 5 = \( \frac{y}{-9} \)
-9 x (7y + 5) = y
(-9 x 7y) + (-9 x 5) = y
-63y - 45 = y
-63y - 45 - y = 0
-63y - y = 45
-64y = 45
y = \( \frac{45}{-64} \)
y = -\(\frac{45}{64}\)

To factor a quadratic expression, apply the FOIL (First, Outside, Inside, Last) method in reverse.

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 - 9)(y + 4)
(y x y) + (y x 4) + (-9 x y) + (-9 x 4)
y² + 4y - 9y - 36
y² - 5y - 36

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

AD = AB + BD