A circular disk with an area of rolls in a circular path. The disk would move in rolls times to finish the path. If the path's length was a circumference of a circle, what would be the imaginary circle's area?
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Let D be the disk and P be the circular path.
The disk had an area of 1 squared unit. We can figure out the disk's circumference with this information.
D A π r 2 r 2 r = 1 = 1 = π 1 = π 1 or π 1 or π π
With the radius given, we can solve for D C or the disk's circumference.
D C = 2 π r = 2 π ( π π ) = 2 π
It was said that P C or the path's length is π times D C .
P C = D C π = ( 2 π ) π = 2 π 3
We turn P into a circle. If the path's length is P C or the circle's circumference, we can now get P A or the area of the circle.
2 π r r r = 2 π 3 = 2 π 2 π 3 = π
P A = π r 2 = π ( π ) 2 = π 2
So the area of the imaginary circle is π 2 which is also equal to π π 5 .
π 2 ⋅ π π = π π 2 ⋅ π = π 2 1 π 2 ⋅ π 2 1 = π 2 1 π 2 5 = π π 5
Since π π is equals to 1 , we don't actually change the value when it's multiplied to π 2 .