Angles-Polygons-Triangles- Quadrilaterals Angles If two lines cross we say they INTERSECT. If two lines in the same plane do not intersect, we say they are PARALLEL. If two lines make square corners at the point of intersection we say the lines are PERPENDICULAR. Angles made by perpendicular lines are called RIGHT ANGLES.

Angles continued Two right angles form a STRAIGHT ANGLE. An angle smaller than a right angle is called an ACUTE ANGLE. An angle greater than a right angle is called an OBTUSE ANGLE. The degree measure of a CIRCLE is 360 degrees.

POLYGONS Memorize the following (on p. 5): Triangle Quadrilateral Pentagon Hexagon Heptagon Octagon Nonagon Decagon Undedecagon Dodecagon 3 sides 4 sides 5 sides 6 sides 7 sides 8 sides 9 sides 10 sides 11 sides 12 sides

POLYGONS CONTINUED If a polygon has an indentation, it is call a CONCAVE POLYGON. Any polygon which does not have an indentation is call a CONVEX POLYGON. If all sides of a polygon have the same length, the polygon is EQUILATERAL. If all angles of a polygon have the same measure the polygon is EQUIANGULAR. If the polygon has all sides of the same length and all angles of the same measure, it is called a REGULAR POLYGON.

TRIANGLES The SUM of the THREE ANGLES in any triangle is 180 DEGREES. If a triangle has a right angle it is called a RIGHT TRIANGLE. If all angles of a triangle measure less than 90 degrees, the triangle is an ACUTE TRIANGLE. If one angle in a triangle has a measure greater than 90 degrees, the triangle is an OBTUSE TRIANGLE. If two sides of a triangle have equal length, the triangle is an ISOSCELES TRIANGLE. If the lengths of all sides are equal, the triangle is an EQUILATERAL TRIANGLE. If all sides have different lengths, the triangle is a SCALENE TRIANGLE. Design Fun With Polygons