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 -3 and 7. Then, plug these into a set of binomials using the square root of the First variable (y²):

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

The area of a rectangle is equal to its length x width:

a = l x w
a = a x b
a = 9 x 7
a = 63

The sum of the interior angles of a triangle is 180°:
180° = a° + b° + c°
c° = 180° - a° - b°
c° = 180° - 61° - 27° = 92°

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.

5a - 6 < 7 - 7a
5a < 7 - 7a + 6
5a + 7a < 7 + 6
12a < 13
a < \( \frac{13}{12} \)
a < 1\(\frac{1}{12}\)

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 - 8)(y + 1)
(y x y) + (y x 1) + (-8 x y) + (-8 x 1)
y² + y - 8y - 8
y² - 7y - 8