Question 815577: [ Find the area enclosed between two concentric circles of radii 6.3 cm and 8.4 cm. A third concentric circle is drawn outside the 8.4 cm circle so that the area enclosed between it and 8.4 cm circle is the same as that between the two inner circles. Find the radius of the third circle correct up to two decimal places. ]
Answer by TimothyLamb(4379)   (Show Source):
You can put this solution on YOUR website! a = pi * r^2
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inner ring difference area (d):
d = pi * 8.4^2 - pi * 6.3^2
d = pi * 8.4^2 - pi * 6.3^2
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Answer 1:
d = 96.98 sq.cm
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outer ring difference area (d):
d = 96.98 sq.cm = pi * r^2 - pi * 8.4^2
96.98 = pi * r^2 - pi * 8.4^2
96.98 = pi * r^2 - pi * 70.56
96.98 = pi * ( r^2 - 70.56 )
96.98/pi = r^2 - 70.56
96.98/pi + 70.56 = r^2
r^2 = 101.43
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Answer 2:
r = 10.07 cm
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