Issue 21: Geometry

By Miyu:
WELL... It is the hot humid summer but we still have to keep studying to keep up the good work. More Geometry （ｏ。ｏ；）☆⌒(*＾-°)v
So... ISSUE 21: Geometry. 
Arc Length: Distance along an arc measured in linear units
 <<< Here's a picture I found on google that could help you. (This isn't a photo made by me, just a good photo to use)

Sector of a circle: The region inside a circle bounded by two radii of the circle and their intercepted
arc.
 <<<More good pictures and information.
Incenter of the triangle: When all 3 angels of a triangle are bisected, the point of concurrency.
If a line bisects an angle of a triangle,  then it divides the opposite side proportionally to the other 2 sides of the triangle.
If perpendicular bisectors are drawn for every side of a triangle, the point of concurrency is the circumcenter of the triangle.
The circumcenter lies at the center of the circle that contains the three vertices of the triangle. Any circle that contains all the vertices of a polygon is called a circumscribed circle. Any Polygon with each vertex on a circle is an inscribed polygon
Theorem 39-1: If one side of a triangle is longer than the other side, then the angle opposite the first side is larger than the angle opposite the first side is larger than the angle opposite the second side.

Theorem 39-2: If one angle of a triangle is larger than another angle, then the side opposite the first angle is longer than the side opposite the second angle.

Theorem 39-3: Exterior Angle Inequality Theorem: The measure of an exterior angle is greater than the measure of either remote interior angle.

Theorem 39-4: The sum of the length of any two sides of a triangle must be greater than the length of the third side.

Postulate 19: If two polygons are congruent, then they have the same area.
Postulate 20: The area of a region is equal to the sum of the areas of its nonoverlapping parts.
Theorem 40-1: Hinge Theorem- If two sides of one triangle are congruent to two sides of another triangle and the included angle of the first triangle is greater than the included angle of the second triangle, then the third side of the first triangle is longer than the third side of the second triangle.
Theorem 40-2: Converse of the Hinge Theorem: If two sides of one triangle are congruent to two sides of another triangle and  the third side of the first triangle is longer than the third side of the second triangle.

**EDIT**
Measure of central angle = Measure of arc. 
(A friend assured me... LOL)