Triangles Part 1

The sum of the angles in a triangle is always equal to: 180°

Classification By Angle Acute A triangle that has all 3 acute angles Obtuse A triangle with one obtuse angle and 2 acute angles Right A triangle with 1 right angle and 2 acute angles The two acute angles must = 90° therefore they are complimentary Equiangular A triangle with all 3 angles congruent They must each = 60 °

Classification by Sides Scalene All three sides have different lengths Isosceles Two sides have the same length Equilateral All three sides have the same length

Isosceles Triangles AB = CB and <A = < C Leg Base

Equilateral Triangle An equilateral triangle is also equiangular. An equiangular triangle is also equilateral AB = BC = AC<A = <B = <C

Classify each triangle by its angles and sides. Equilateral Scalene, Right Isosceles, Acute Isosceles, Obtuse Scalene, Acute Isosceles, Right

Using the Distance Formula to classify triangles by their sides Find the measure of the sides of triangle DCE, then classify the triangle by sides.

You Try Find the measure of the sides of  RST. Classify the triangle by sides.   RST is Scalene

Find the missing Values Find x and the measure of each side of an equilateral triangle RST if:

You Try Find d and the measure of each side of an equilateral triangle KLM if:

One more! (This one is a little different) Find x and the measure of all sides if  COW is isosceles, with CO=CW, and

Finding the Measure of Missing Angles

The sum of the angles in a triangle is always equal to: 180°

Examples Find X:

Exterior Angle Theorem The measure of an exterior angle of a triangle is equal to the sum of the remote interior angles. Exterior Angle: An angle formed when one side of a triangle is extended Remote Interior Angles: The interior angles of the triangle that are not adjacent to the exterior angle

Proof of Exterior Angle Theorem

Bigger Picture Find all missing angles