Angles around a line add up to 180°. Angles around a point add up to 360°. When two lines intersect, adjacent angles are supplementary (they add up to 180°) and angles across from either other are vertical (they're equal).

The formula for area is πr². Radius is circle \( \frac{diameter}{2} \):

r = \( \frac{d}{2} \)
r = \( \frac{8}{2} \)
r = 4
a = πr²
a = π(4²)
a = 16π

A triangle is a three-sided polygon. It has three interior angles that add up to 180° (a + b + c = 180°). An exterior angle of a triangle is equal to the sum of the two interior angles that are opposite (d = b + c). The perimeter of a triangle is equal to the sum of the lengths of its three sides, the height of a triangle is equal to the length from the base to the opposite vertex (angle) and the area equals one-half triangle base x height: a = ½ base x height.

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

a = l x w
a = a x b
a = 8 x 9
a = 72

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

y² - 10y + 16 = 0
(y - 2)(y - 8) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (y - 2) or (y - 8) must equal zero:

If (y - 2) = 0, y must equal 2
If (y - 8) = 0, y must equal 8

So the solution is that y = 2 or 8