Grade 7 Geometry: Triangle Angles

Worked examples

Real problems from the practice worksheets, solved one step at a time.

1. Example 1

   Two angles of a triangle measure 34° and 28°. What is the measure of the third angle, in degrees?

   1. The three angles of any triangle add up to 180°.
   2. 180° − 34° − 28° = 118°.

   Answer: 118

2. Example 2

   The three angles of a triangle measure x°, (x + 9)°, and (x + 39)°. What is the value of x?

   1. The three angles of a triangle add up to 180°.
   2. x + (x + 9) + (x + 39) = 3x + 48 = 180
   3. 3x = 132
   4. x = 132 ÷ 3 = 44

   Answer: 44

3. Example 3

   A right triangle has one acute angle that measures 41°. What is the measure of the other acute angle, in degrees?

   1. The angles of a triangle add up to 180°, and the right angle is 90°.
   2. 180° − 90° − 41° = 49°.

   Answer: 49