A trapezoid is a quadrilateral with one set of parallel sides.

To multiply monomials, multiply the coefficients (the numbers that come before the variables) of each term, add the exponents of like variables, and multiply the different variables together.

(5a)(4ab) - (9a²)(9b)
(5 x 4)(a x a x b) - (9 x 9)(a² x b)
(20)(a¹⁺¹ x b) - (81)(a²b)
20a²b - 81a²b
-61a²b

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

y² + 7y + 12 = 0
(y + 3)(y + 4) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (y + 3) or (y + 4) must equal zero:

If (y + 3) = 0, y must equal -3
If (y + 4) = 0, y must equal -4

So the solution is that y = -3 or -4

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 - 5)(y - 2)
(y x y) + (y x -2) + (-5 x y) + (-5 x -2)
y² - 2y - 5y + 10
y² - 7y + 10

An acute angle measures less than 90°, a right angle measures 90°, and an obtuse angle measures more than 90°.