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Working Backwards

Working Backwards. Finding Circumference From Area. Finding Area from Circumference: Not Too Difficult. We are familiar with the steps for finding Area if we are given the circumference The missing information for solving for the area of a circle is always radius, because Pi is always 3.14.

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Working Backwards

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  1. Working Backwards Finding Circumference From Area

  2. Finding Area from Circumference: Not Too Difficult • We are familiar with the steps for finding Area if we are given the circumference • The missing information for solving for the area of a circle is always radius, because Pi is always 3.14

  3. Where do we get our radius? • If you have a circumference, you can find the diameter. • C = • C ÷ = x D ÷ π • C ÷ = D • Half of the Diameter = Radius • D= 2r • Once you have the Radius, sub it into the equation

  4. So, what if we start with the Area? • If we have the area, and we need to find the circumference, what is the missing number that we must find to solve for? • We need the Diameter to find circumference, so to find the diameter if we are given Area, we have to work backwards from the area, and find the specific radius. • This is harder than it seems. What might be a problem in solving this?

  5. If the area of a circle is 19.625 cm², then what is the circumference of the circle?We need to take area, and work backwards to find r19.625cm² = 19.625 cm² ÷ π = ÷ π19.625 cm²÷ π = 6.25 cm² = Okay… now what?

  6. The Tricky Part is the We need radius (r) and we have . To get back to an r, we need to do the opposite operation of squares…. Welcome back, square root!!

  7. So, we continue the Equation, using square root to change the 19.625cm² = 19.625 cm² ÷ π = ÷ π19.625 cm²÷ π = 6.25 cm² = √(6.25cm²) = √()2.5 cm = r

  8. Now it’s easy to find the Circumference:if r = 2.5 cm 2x r = D 2 x 2.5 cm = D 5 cm = D C= π x DC = 3.14 x 5 cmC = 15. 70 cm

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