If the area of a circle is 81π, then the diameter of the circle isA、9B、18C、36

游客2024-01-14  18

问题 If the area of a circle is 81π, then the diameter of the circle is

选项 A、9
B、18
C、36
D、9π
E、18π

答案 B

解析 The formula for the area of a circle is πr2. Therefore, the radius of this circle is the square root of 81, or 9. The diameter is twice the radius, so 18.
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