3 •How do you find the degree of an angle? You use a protractor! It’s a small, semi-circular tool that contains markings from 0 to 180 degrees. The way you use it is to line up one of the angle’s rays on the 0 degree line along the flat, bottom part of the protractor.
4 •How do you find the degree of an angle? Then you look where the other ray hits the markings. Sometimes you have to extend the line so it’s long enough to reach the markings. You can do that using the straight edge of the protractor; just line it up and make the line long enough so it reaches the markings!
7 •What are acute, obtuse, and right angles? An angle is a measure of how much space there is between two lines, measured in degrees or radians. A right angle measures exactly 90 degrees, and makes an L shape. Any angle that measures more than 90 degrees is called an obtuse angle.
8 •What are acute, obtuse, and right angles? An angle that is less than 90 degrees is called an acute angle. For example, when it is exactly three o’clock, the hour and minute hands make a right angle. When it is 3:10, the hands make an acute angle. When it is four o’clock, the hands make an obtuse angle.
11 •What is a ray?In geometry, lines go on forever. A ray is like a line that only goes on forever in one direction. We draw it as a line segment with an arrow on the end. An angle is made up of two rays.
17 RadiusThe distance around a circle is called its circumference. The distance across a circle through its center is called its diameter. We use the Greek letter (pronounced Pi) to represent the ratio of the circumference of a circle to the diameter.
18 RadiusIn the last lesson, we learned that the formula for circumference of a circle is: . For simplicity, we use = We know from the last lesson that the diameter of a circle is twice as long as the radius. This relationship is expressed in the following formula: .
19 RadiusThe area of a circle is the number of square units inside that circle. If each square in the circle to the left has an area of 1 cm2, you could count the total number of squares to get the area of this circle. Thus, if there were a total of squares, the area of this circle would be cm2
20 RadiusHowever, it is easier to use one of the following formulas: or where is the area, and is the radius. Let's look at some examples involving the area of a circle. In each of the three examples below, we will use = 3.14 in our calculations.