Term | Definition |
point | has no length, width or thickness |
line | has length but no width or thickness |
plane | has length and width but no thickness |
straight line segment | the part of a straight line between two of its points |
midpoint | if a line is divided into two equal parts, this is the point of division |
congruent segments | two segments having the same length are said to be this |
circle | the set of all points in a plane that are the same distance from a point |
circumference | distance around a circle |
radius | a segment that joins the center of a circle to a point on the circle |
central angle | an angle formed by two radii |
chord | a segment joing any two points on a circle |
diameter | a chord through the center of a circle |
arc | a continuous part of the circle |
semicircle | an arc measuring one half the circumference of a circle |
congruent circles | circles having congruent radii are said to be this |
angle | the figure formed by two rays with a common end point |
acute angle | an angle whose measure is less than 90 degrees is said to be an |
right angle | an angle that measures 90 degrees is said to be a |
obtuse angle | an angle that measures more than 90 degrees and less than 180 degrees is said to be an |
straight angle | an angle that measures 180 degrees is said to be a |
reflex angle | an angle whos measure is more thatn 180 degrees and less than 360 degrees is said to be a |
congruent angles | two angles that have the same number of degrees are said to be |
angle bisector | a line that divides an angle into two equal parts |
perpendicular | lines, rays or segments that meet at right angles are said to be |
perpendicular bisector | a segment that is bisects and is perpendicular to another segment |
polygon | a closed plane figure bounded by straight line segments at the sides |
pentagon | a polygon with 5 sides |
triangle | a polygon having three sides |
vertex | the point at which two of sides of a polygon meet |
scalene | a triangle that has no congruent sides |
isosceles | a triangle that has at last two congruent sides |
legs | the equal sides of an isosceles triangle |
base angles | the angles on either side of the base of an isosceles triangle |
base | the side of an isosceles triangle that are not the legs |
equilateral | a triangle that has three congruent sides |
right triangle | a triangle that has a right angle |
obtuse triangle | a triangle that has an obtuse angle |
acute triangle | a triangle that has three acute angles |
angle bisector of a triangle's angle | a segment or ray that bisects the angle of triangle and extends to the opposite side |
median of a triangle | a segment from a vertex to the midpoint of the opposite side |
perpendicular bisector of a triangle's side | a line that bisects and is perpendicular to a side of a triangle |
altitude of a triangle | a segment from the vertex of a triangle to the opposite side |
outside the triangle | in an obtuse triangle, an altitude drawn on either side of an obtuse angle falls here |
adjacent angles | two angles which have the same vertex and a common side |
vertical angles | two nonadjacent angles formed by two intersecting lines |
complementary angles | two angles whose measures add to 90 degrees |
supplementary angles | two angles whose measures add to 180 degrees |
transitive postulate | things equal to the same things are equal to each other |
subtitution postulate | a quantity may be substituted for its equal in any expression or equation |
partition postulate | the whole equals the sum of its parts |
reflexive or identity postulate | any quantity equals itself |
addition postulate | if equals are added to equals, the sums are equal |
subtraction postulate | if equals are subtracted from equals, the differences are equal |
multiplication postulate | if equals are multiplied by equals, the products are equal |
division postulate | if equals are divided by equals, the quotients are equal |
powers postulate | like powers of equals are equal |
postulate 10 | like roots of equals are equal |
one | the number of straight lines that can be drawn through any two points |
theorem | a statement, which proved, can be used to prove other statements |
CPCTC | congruent parts of congruent triangles are congruent |
SAS | a way of proving two triangles are congruent when they have two sides and the included angle congruent to each other |
orthocenter | the intersection point of a triangles altitudes |
incenter | the angle bisectors of a triangle meet at this point |
circumcenter | the perpendicular bisectors of the triangle meet at this point |
centroid | the intersection point of the three medians in a triangle |