Section Warm-Up
Before we begin this section, let’s see what you already know. These questions are meant to draw on skills learned in previous courses. If you do not remember these concepts, that is okay, we will be reviewing them as we study this lesson.
Think & Click: Section Warm-Up
Complete the Think & Click activity by looking at each problem below, thinking about it, and then clicking on the question to reveal the solution.
What is the circumference of a circle? How do you find the circumference of a circle?
The circumference of a circle is the distance around the circle. To find the circumference, we can use either formula:
C = 2
r
C =d
C = 2
rC =
dFind the circumference of a circle with radius 7 inches.
C = 2r = 2(7) = 14 inches, or approximately 43.98 inches
r = 2(7) = 14 inches, or approximately 43.98 inchesFind the circumference of a circle with diameter 10 centimeters.
C = d = (10) = 10 centimeters, or approximately 31.42 centimeters.
d = (10) = 10 centimeters, or approximately 31.42 centimeters.What is the area of a circle? How do you find the area of a circle?
The area of a circle really means the area enclosed by the circle. It is the square units that are inside the circle. To find the area, we use the formula:
A =r2
A =
r2Find the area of a circle with radius 7 inches.
A = r2 = (7)2 = 49square inches or approximately 153.94 square inches.
r2 = (7)2 = 49square inches or approximately 153.94 square inches.Find the area of a circle with diameter 10 centimeters.
d = 10, r = 5
A =r2 = (5)2 = 25square centimeters or approximately 78.54 square centimeters.
A =
r2 = (5)2 = 25square centimeters or approximately 78.54 square centimeters.