Triangle Congruence and Angle Rules

SSS

If all 3 sides of one triangle match all 3 sides of another, the triangles are the same.

SAS

If 2 sides and the angle between them in one triangle match another, the triangles are the same.

ASA

If 2 angles and the side between them in one triangle match another, the triangles are the same.

AAS

If 2 angles and any one side in one triangle match another, the triangles are the same.

HL

If the longest side and one leg of a right triangle match another, the triangles are the same.

Vertical Angles

Opposite angles where lines cross are equal.

Alternate Interior Angles

Angles inside parallel lines but on opposite sides are equal.

Corresponding Angles

Angles in the same spot on parallel lines are equal.

Linear Pair

Two angles next to each other on a straight line add up to 180°.

Midpoint

A point in the middle that splits a segment into two equal parts.

Angle Bisector

A line that cuts an angle into two equal angles.

Perpendicular Lines

Lines that cross and make a 90° angle.

Right Angle

An angle that is exactly 90°.

Congruent

Same size or length.

Reflexive

A side or angle is equal to itself.

Symmetric

If one side or angle equals another, then the second equals the first.

Transitive

If one side or angle equals a second, and the second equals a third, then the first equals the third.

Substitution

You can swap one side or angle for another equal one.

Isosceles Triangle

If two sides are equal, the angles opposite them are also equal.

Triangle Sum

The 3 angles inside a triangle add up to 180°.

CPCTC

If two triangles are the same, all their matching sides and angles are also the same.