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

r = \( \frac{d}{2} \)
r = \( \frac{10}{2} \)
r = 5
a = πr²
a = π(5²)
a = 25π

The area of a trapezoid is one-half the sum of the lengths of the parallel sides multiplied by the height:

a = ½(b + d)(h)
a = ½(4 + 2)(2)
a = ½(6)(2)
a = ½(12) = \( \frac{12}{2} \)
a = 6

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 equal sign and the answer on the other.

-4y + 7 = \( \frac{y}{4} \)
4 x (-4y + 7) = y
(4 x -4y) + (4 x 7) = y
-16y + 28 = y
-16y + 28 - y = 0
-16y - y = -28
-17y = -28
y = \( \frac{-28}{-17} \)
y = 1\(\frac{11}{17}\)

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.

To factor a quadratic expression, apply the FOIL (First, Outside, Inside, Last) method in reverse.