Notes on Triangles Vertices are labeled with capital

Notes on Triangles

• Vertices are labeled with capital letters. A • The side opposite the vertex is labeled with a corresponding lowercase letter. B c a b C

Facts From Geometry: Triangle sum B • What happens if you place the angles of a A triangle side by side… C

What do these words mean? • Acute • Right • Obtuse

What can you tell me about this triangle? • A right triangle has one angle that measures exactly 90⁰.

What can you tell me about this triangle? • An acute triangle has all angles measuring less than 90⁰.

What can you tell me about this triangle? • An obtuse triangle has one angle that measures greater than 90⁰.

What can you tell me about these triangles? • An isosceles triangle has at least two congruent sides.

Which sides are congruent? • A scalene triangle has no congruent sides.

Which sides are congruent? • An equilateral triangle has three congruent sides. • What about the angles? • An equiangular triangle has three congruent angles. • What is the measure of each angle?

Notation Shape and size. Equal numbers

Congruent Triangles If triangles can be rotated, translated, or reflected to match vertex to vertex, then the triangles are congruent. If triangles are congruent, then all corresponding parts are also congruent (3 angles and 3 sides).

Shortcuts… beginning tomorrow we will see how we can use shortcuts to prove that two triangles are congruent instead of having to prove all 6 corresponding parts are congruent.

Homework Assignment: Study all notes from today!