In this exercise, interact with the arms BD and BE to investigate the relationship between the three adjacent angles on the straight line.

**Warmup**

What is the sum of the adjacent angles of a straight line?

**Activity #1**

**Estimate the Size of an Angle.**

- Estimate the degree measure of each indicated angle.

**Activity #2**

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**Measuring an Angle.**

- Drag the red point to draw a small half-circle in the middle of one side.
- Use to cut a straight line, starting from the center of the half-circle, all the way across the paper to make 2 separate pieces. (Your cut does not need to be perpendicular to the side of the paper.)
- On each of these two pieces, measure the angle that is marked by part of a circle. Label the angle measure on the piece.

(1.) What do you notice about these angle measures?

(2.) Clare measured 70 degrees on one of her pieces. Predict the angle measure of her other piece.

- In the applet below, draw a small quarter-circle in one of the corners.
- Repeat the previous steps to cut, measure, and label the two angles marked by part of a circle.

(3.) What do you notice about these angle measures?

(4.) Priya measured 53 degrees on one of her pieces. Predict the angle measure of her other piece.

**Challenge #1**

(1.) Use the protractor in the picture to find the measure of angles

(2.) Explain how to find the measure of angle without repositioning the protractor.

**Challenge #2**

(1). Use the protractor in the picture to find the measure of angles

(2). Explain how to find the measure of angle without repositioning the protractor.

**Quiz Time**

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