SOLUTION: The arc length of a circle is 18π and the radius of the same circle is 36 cm. How big is the central angle that subtends the arc?

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Question 1138270: The arc length of a circle is 18π and the radius of the same circle is 36 cm. How big is the central angle that subtends the arc?
Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!
The arc length of a circle is l=18pi and the radius of the same circle is 36cm.
How big is the central angle that subtends the arc?
l=2pi%2Ar%28alpha%2F360%29
18pi=2pi%2A36%28alpha%2F360%29
18pi%2F%2872pi%29=%28alpha%2F360%29
1%2F4=alpha%2F360..... both sides multiply by 360
360%2F4=alpha
alpha=90

or this way:
The arc length of a circle is l=18pi which is a portion of the circumference C=2rpi
if the radius of the same circle is 36cm,+2rpi=2%2A36pi=72pi
find ratio l%2FC=18pi%2F72pi=1%2F4=> central angle is 1%2F4 of full angle which is 360%2F4=90 degrees