TRIANGLESSPI 6.4.2 I CAN identify and find

missing angles measures in triangles.

A triangle is a closed figure with three line segments and three angles.

Classify TrianglesSides AnglesEquilateral Acute

Isosceles Obtuse

Scalene Right

Equilateral Triangle

ALL three sides and angles equal in measure. In the figure below , the slash marks indicate equal measure.

Isosceles Triangle

At least 2 sides/angles have equal measure. In the figure below , the slash marks indicate equal measure.

62 62

Scalene Triangle

All three sides of different measures (no equal sides).

Right Triangle

contains a right angle (90 ͦ)

Obtuse Triangle

Contains at least 1 obtuse angle (greater than 90° but less than 180°)

123

Acute Triangle

All acute angles (less than 90°)

The sum of the measures of the angles of any triangle always equals 180 degrees.

A + B + C = 180°

This is a proof that the angles in a triangle equal 180°:

The top line (that touches the top of the triangle) is running parallel to the base of the triangle. A straight line or angle equals 180 degrees.

A + B + C = 180°

Find the missing angle c?

Question 1

The measure of two angles are 45° and 45 °.

A. Acute

B. Right

C. Obtuse

D. Cannot be determined

Question 2

The measure of two angles are 15 ° and 47 °.

A. Acute

B. Right

C. Obtuse

D. Cannot be determined

Question 3

The measures of two angles are 53 ° and 76 ° .

A. Acute

B. Right

C. Obtuse

D. Cannot be determined

Question 4

The measure of one angle is 18 °.

A. Acute

B. Right

C. Obtuse

D. Cannot be determined

Question 5

The measure of one angle is 90 degrees.A. Acute

B. Right

C. Obtuse

D. Cannot be determined

Question 6

The measure of one angle is 115 degrees. A. Acute

B. Right

C. Obtuse

D. Cannot be determined

Question 7

The sides measures of a triangle is 10 cm, 5 cm, and 10 cm. Classify this triangle?

A. Scalene

B. Acute

C. Isosceles

D. Obtuse

Find the missing angle c?

Find the missing angle c?

Find the missing angle b?