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 -21 as well and sum (Inside, Outside) to equal -4. For this problem, those two numbers are -7 and 3. Then, plug these into a set of binomials using the square root of the First variable (y²):

y² - 4y - 21
y² + (-7 + 3)y + (-7 x 3)
(y - 7)(y + 3)

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 - 2a = 5a

Perimeter is equal to the sum of the four sides:

p = a + b + c + d
p = 8 + 5 + 4 + 5
p = 22

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 > sign and the answer on the other.

b - 4 > \( \frac{b}{5} \)
5 x (b - 4) > b
(5 x b) + (5 x -4) > b
5b - 20 > b
5b - 20 - b > 0
5b - b > 20
4b > 20
b > \( \frac{20}{4} \)
b > 5

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

y² - 4 = 0
(y - 2)(y + 2) = 0

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

If (y - 2) = 0, y must equal 2
If (y + 2) = 0, y must equal -2

So the solution is that y = 2 or -2