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.

A circle is a figure in which each point around its perimeter is an equal distance from the center. The radius of a circle is the distance between the center and any point along its perimeter. A chord is a line segment that connects any two points along its perimeter. The diameter of a circle is the length of a chord that passes through the center of the circle and equals twice the circle's radius (2r).

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

-9a + 8y = 5a + 9y - 6
-9a = 5a + 9y - 6 - 8y
-9a - 5a = 9y - 6 - 8y
-14a = y - 6
a = \( \frac{y - 6}{-14} \)
a = \( \frac{y}{-14} \) + \( \frac{-6}{-14} \)
a = -\(\frac{1}{14}\)y + \(\frac{3}{7}\)

A parallelogram is a quadrilateral with two sets of parallel sides. Opposite sides (a = c, b = d) and angles (red = red, blue = blue) are equal. The area of a parallelogram is base x height and the perimeter is the sum of the lengths of all sides (a + b + c + d).

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