Reasoning about angles in a triangle

1. Rotate triangle ABC 180° around the midpoint of side AC. Label the new vertex D.

2. Rotate triangle ABC 180° around the midpoint of side AB. Label the new vertex E.

3. Look at angles 3, 4, and 7. Without measuring, write what you think is the sum of the measures of these angles. Explain or show your reasoning.

Rotate triangle ABC 180° around the midpoint of side AB. Label the new vertex E.

1. Is the measure of angle 3 equal to the measure of any angle in triangle ABC? If so, which one? If not, how do you know? Use numbers to represent angles.

1. Rotate triangle ABC 180° around the midpoint of side AC. Label the new vertex D.

2. Is the measure of angle 7 equal to the measure of any angle in triangle ABC? If so, which one? If not, how do you know? Use numbers to represent angles.

Is it always true that the sum of the angles in a triangle is 180°?

Find the measure of the missing angle in the Figure shown

Find the measure of the missing angle in Figure 2

Find the measure of the missing angle in Figure 3

Find the measure of the missing angle in Figure 4

Here is a diagram of triangle DEF. Find the measures of angles q, r, and s.

Here is a diagram of triangle DEF. Find the sum of the measures of angles q, r, and s.