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

a = ½(b + d)(h)
a = ½(6 + 8)(3)
a = ½(14)(3)
a = ½(42) = \( \frac{42}{2} \)
a = 21

To solve this equation, isolate the variable for which you are solving (b) on one side of the equation and put everything else on the other side.

-6b - 9x = -9b - 8x - 2
-6b = -9b - 8x - 2 + 9x
-6b + 9b = -8x - 2 + 9x
3b = x - 2
b = \( \frac{x - 2}{3} \)
b = \( \frac{x}{3} \) + \( \frac{-2}{3} \)
b = \(\frac{1}{3}\)x - \(\frac{2}{3}\)

The circumference of a circle is the distance around its perimeter and equals π (approx. 3.14159) x diameter: c = π d. The area of a circle is π x (radius)² : a = π r².

The surface area of a cube is (2 x length x width) + (2 x width x height) + (2 x length x height):

sa = 2lw + 2wh + 2lh
sa = (2 x 3 x 5) + (2 x 5 x 6) + (2 x 3 x 6)
sa = (30) + (60) + (36)
sa = 126