There are two angles of a polygon: interior and exterior. An interior angle of a polygon are angles inside a polygon formed by the intersection of two sides. An exterior angle of a polygon are angles between any side of a shape, and a line extended from the next side. Each exterior angle forms a linear pair with one of the interior angles. The sum of an interior angle is 5=(n-2)180, and the sum of an exterior angle is 360/n.
Thereom 6.3 states, “If a quadrilateral is a parallelogram, then its opposite sides are congruent.” If JKLM is a parallelogram, then JK is congruent to ML and JM is congruent to KL. In example 7, if ABCD is a parallelogram, solve for the value of x. AB= 6x+2 and CD=4x+12. First, set the equations equal to each other: 6x+2=4x+12. Next, subtract 2 on both sides: 6x=4x+10. Then, subtract 4x on both sides: 2x=10. Finally, divide 2 by 10 to get 5 for the value of x.
Jillian Pou Geometry Blog 