### plane

a flat surface made up of points; has no depth and extends indefinitely in all directions (undefined term)

### opposite rays

two rays are opposite to each other iff they have the same endpoint and they are collinear

### converse

the statement formed by exchanging the hypothesis and conclusion of a conditional statement

### inverse

the statement formed by negating both the hypothesis and conclusion of a conditional statement

### contrapositive

the statement formed by negating both the hypothesis and conclusion of the converse of a conditional statement

### corresponding angles (postulate)

if two parallel lines are cut by a transversal, then the corresponding angles are congruent

### converse of corresponding angles (postulate)

if corresponding angles are congruent, then the lines are parallel

### alternate interior angle (theorem)

if two parallel lines are cut by a transversal, then each pair of alternate interior angles is congruent

### consecutive interior angle (theorem)

if two parallel lines are cut by a transversal, then each pair of consecutive interior angles is supplementary

### alternate exterior angle (theorem)

if two parallel lines are cut by a transversal, then each pair of alternate exterior angles is congruent

### third angle theorem

if two angles of one triangle are congruent to two angles of a second triangle, then the third angles of the triangles are congruent

### exterior angle theorem

the measure of an exterior angle of a triangle is equal to the sum of the measures of the two remote interior angles

### sss

if the sides of one triangle are congruent to the sides of a second triangle, then the triangles are congruent

### sas

if two sides and the included angle of one triangle are congruent to two sides and the included angle another triangle, then the triangles are congruent

### asa

if two angles and the included side of one triangle are congruent to two angles and the included side of another triangle, then the two triangles are congruent

### aas

if two angles and a non-included side of one triangle are congruent to the corresponding two angles and side of a second triangle, then the two triangles are congruent

### HL

if the hypotenuse and a leg of one right triangle are congruent to the hypotenuse and corresponding leg of another right triangle, then the triangles are congruent

### isosceles triangle theorem

if two sides of a triangle are congruent, then the angles opposite those sides are congruent

### perpendicular bisector (of a line segment)

a line that cuts through another line segment at its midpoint and bisects it at a 90° angle

### triangle inequality theorem

in a triangle, the sum of the measures of two sides is greater than the measure of the third side

### hinge theorem

if two sides of one triangle are congruent to two sides of another triangle and the included angle in the first triangle is greater than the included angle in the second triangle, then the remaining side of the first triangle is greater than the remaining side of the second triangle

### converse of 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 greater than the third side of the second triangle, then the angle opposite the third side in the first triangle is greater than the angles opposite the third side in the second triangle