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Triangle sum theorem

The sum of the measures of the interior angles of a triangle is 180°

Exterior angle theorem

measure of the exterior angle is equal to the sum of the remote interior angles

Third angles theorem

If two angles of one triangle are congruent to two angles of a second triangle, then the third angles are also congruent

SSS Congruence postulate

if 3 sides of 1 triangle are are congruent to 3 sides of another triangle, then the 2 triangles are congruent

SAS Congruence postulate

if 2 sides and the included angle of 1 triangle are congruent to 2 sides and the included angle of another triangle, then the 2 triangles are congruent

ASA Congruence postulate

if 2 angles and the included side of one triangle are congruent to 2 angles and the included side of another triangle, then the 2 triangles are congruent

AAS Congruence theorem

if two angles and a side of one triangle are congruent to the corresponding angles and side of another triangle, then they are congruent

HL Congruence theorem

if in two right triangles, the hypotenuse and leg of one are congruent to the hypotenuse and leg of the other, then the triangles are congruent to each other

isosceles triangle theroem

if 2 sides of a triangle are congruent, then the angles opposite these sides are also congruent