Skill13 circles
- 1. Circles Vocabulary for circles: radius—the distance from the center to the edge Diameter—the distance all the way across the circle through the center Π– pi—a number found in formulas for circle area and circumference (perimeter) which has a value of 3.14. This number will be given on the formula page. Circumference—the distance around the circle—think of this like the perimeter of the circle Area—the amount of space inside the circle. Look at the formulas for Circumference Sometimes you will be given the radius so use C = 2 times pi times radius If you are given the diameter, use C = pi times diameter. Just double the radius to get the diameter or take half of the diameter to get the radius.
- 2. Look at page 92 in the book. Here are some sample problems. In this problem, we are given the radius. In this problem, we are given the diameter.
- 3. The problems below require us to work backward. That is we are not asked to find the area. It is given. Rather, we put all the values we know in the formula and find the one we don’t know. In #4, we are given the circlumference and asked to find the radius.
- 4. Circles or halves of circles can be attached to other figures to make a new composite shape. See the examples below. To find the area of the composite shape, add the parts together. The radius is half the length of the rectangle part in the figure.
- 5. There are a lot of practice problems on the pages in Skill 13 part of your book. Since you are having to work on your own, turn to page 95a, 95b, and 95c to see many problems that I have worked out. The problems come from pages 93, 94, and 95. Try to match up the Roman numbers I, II, III, IV, V, VI, etc. to see the original problem. There is an answer page for all the problems but again try to match up the problem numbers. Some are for triangles, trapezoids, parallelograms, as well as circles. I also drew pictures of a trapezoid and a parallelogram at the top of page 95a. The formulas for these figures are on the Math Test formula page. However, I don’t think they are likely to be on the test.