2.1: Estimating Angle Measures
Estimate the degree measure of each indicated angle.
Let’s look at some special pairs of angles.
Estimate the degree measure of each indicated angle.
Your teacher will give you two small, rectangular papers.
Use the protractor in the picture to find the measure of angles:
Explain how to find the measure of angle $ACD$ without repositioning the protractor.
Use the protractor in the picture to find the measure of angles:
Explain how to find the measure of angle $KOM$ without repositioning the protractor.
Clare started with a rectangular piece of paper. She folded up one corner, and then folded up the other corner, as shown in the photos.
Can you explain why the bottom angle always has to be 90 degrees? Hint: the third photo shows Clare’s paper, unfolded. The crease marks have dashed lines, and the line where the two paper edges met have a solid line. Mark these on your own paper as well.
If two angle measures add up to $90^\circ$, then we say the angles are complementary. Here are three examples of pairs of complementary angles.
If two angle measures add up to $180^\circ$, then we say the angles are supplementary. Here are three examples of pairs of supplementary angles.
Two angles are complementary to each other if their measures add up to $90^\circ$. The two acute angles in a right triangle are complementary to each other.
Two angles are supplementary to each other if their measures add up to $180^\circ$.
For example, angle $ABC$ is supplementary to angle $CBD$, because they add up to a straight angle, which has measure $180^\circ$.