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 + 3)
(y x y) + (y x 3) + (9 x y) + (9 x 3)
y² + 3y + 9y + 27
y² + 12y + 27

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

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

a² - a - 12 = 0
(a + 3)(a - 4) = 0

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

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

So the solution is that a = -3 or 4

A right angle measures 90 degrees and is the intersection of two perpendicular lines. In diagrams, a right angle is indicated by a small box completing a square with the perpendicular lines.

A monomial contains one term, a binomial contains two terms, and a polynomial contains more than two terms.