Step 1: Find the unknown angle of the triangle

NOTE: The sum of the angle measures in a triangle is 180 degrees.

EXAMPLE: 42 + 42 + x = 180

x = 180 - 84

x = 96

Step 2: Record the given measurement of each angle or use a protractor to measure each of the 3 interior angles of the given triangle.

Step 3: Recall the Classification of the triangle by the angles

NOTE: Classify the triangle according to the measurement and the type of angles.

**Acute triangle:** A triangle having all acute angles (less than 90°) in its interior

**Right triangle:** A triangle that has a right angle in its interior

**Obtuse triangle:** A triangle having an obtuse angle (greater than 90° but less than 180°) in its interior.

Step 4: Distinguish if the angles are right, acute or obtuse according to their measurements.

EXAMPLE: The triangle has one obtuse angle, so it is an obtuse triangle.