by Guest » Sun Jul 13, 2014 7:38 am
"I used Pi x d^2 / 4 for area and took Pi as 3.142 in above"
I had forgotten that the diameter could be squared.
One question:
Did you divide by 4 because of squaring diameter ?
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In the above I am just using the standard formula for the area of a circle.....
If we are given the diameter of the circle then tha area is (Pi x d^2 / 4)
Or in words Pi times d squared, divided by 4......
Or said the other way around.....Pi divided by 4, times d squared.....
Both are the same....Just rearranged and we are given the diameter so don't bother using the radius.
If we are working in terms of the circle radius.....the radius is half of the diameter = (d / 2).
and the standard formula for the area of a circle using radius is Pi x radius squared = Pi x r^2
Since r is d/2 then r^2 is (d/2)^2.....read as "d" over "2" all squared...to work this out you have to square the "d" and the "2" ... the top and bottom numbers of the fraction.
This gives (d^2) / (2^2) = (d^2) / (4) = (d^2) / 4.
So Pi x r^2 becomes Pi x (d^2) / 4 .... or written the other way around .... (Pi / 4) x d^2.