Triangles Facts

Triangles Facts

1. Triangles Categorized by Angles

   • Right: 90* angle
   • Acute: angle less than 90*, more than 0*
   • Obtuse: angle more than 90*, less than 180*
   • All angles add up to equal 180*
   • Exterior Angle Theorem: The measure of an exterior angle is equal to the sum of 2 interior angles

2. Triangles Categorized by Side Lengths

   • Equilateral: all sides have the same length
   • Isosceles: 2 sides have the same lenght
   • Scalene: No sides are the same length

3. Congruency

   • Triangles can be congruent by angles and side lengths
   • SSS: All 3 side lengths congruent
   • SAS: 2 sides and angle between them are congruent
   • ASA: 2 angles and side between them are congruent
   • AAS: 2 angles and unrelated side are congruent
   • Right Triangle Congruence
     • HL: The hypotenuse and a leg of a right triangle are congruent
     • LL: Both legs of a right triangle are congruent
     • HA: The hypotenuse and an acute angle of a right triangle are congruent
     • LA: A leg and an acute angle of a right triangle are congruent
   • Base Angle Theorem: If 2 sides of a triangle are congruent, the angles opposite of them are congruent

4. Triangle Mid-Segment: a line segment that connects 2 sides of a triangle and is parallel to the 3rd line and is half as long

5. Finding Proportions: seeing if 2 fractions are the same by cross multiplying

6. Side Splitter Theorem: If a line intersect 2 sides of a triangle and is parallel to the 3rd side, it divides the 2 sides proportionally