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

a² - a - 2 = 0
(a + 1)(a - 2) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (a + 1) or (a - 2) must equal zero:

If (a + 1) = 0, a must equal -1
If (a - 2) = 0, a must equal 2

So the solution is that a = -1 or 2

A line segment is a portion of a line with a measurable length. The midpoint of a line segment is the point exactly halfway between the endpoints. The midpoint bisects (cuts in half) the line segment.

The surface area of a cylinder is 2πr² + 2πrh:

sa = 2πr² + 2πrh
sa = 2π(9²) + 2π(9 x 6)
sa = 2π(81) + 2π(54)
sa = (2 x 81)π + (2 x 54)π
sa = 162π + 108π
sa = 270π

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 - 4)(y - 6)
(y x y) + (y x -6) + (-4 x y) + (-4 x -6)
y² - 6y - 4y + 24
y² - 10y + 24

The formula for area is πr²:

a = πr²
a = π(4²)
a = 16π