## 20 terms · Chapter 4 (McDougall Littell) Geometry terms, theorems, postulates, etc.

### Triangle Inequality Theorem

The sum of the lengths of any two sides of a triangle is greater than the length of the third side

### SSS

If three sides of a triangle are congruent to three sides of another 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 of 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 triangles are congruent

### AAS

If two angles and a NON-included side of one triangle are congruent to the corresponding parts of another triangle, then the triangles are congruent

### HL

If the hypotenuse and a leg of one right triangle are congruent to the corresponding parts of another right triangle, then the triangles are congruent. *Only for use of right triangles

### Perpendicular Bisector Theorem

If a point is on the perpendicular bisector of a segment, then the point is an equal distance from the endpoints of the segment

### Isosceles Triangle Theorem

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

### Converse of Isosceles Triangle Theorem

If two angles of a triangle are congruent, then the sides opposite the angle are congruent

### altitude of a triangle

perpendicular segment from a vertex to the line that contains the opposite side

### CPCTC

Corresponding parts of congruent triangles are congruent; once two triangles have been proven congruent (by using SSS, SAS, ASA, AAS, or HL), then we can conclude its parts are congruent through CPCTC