Bullseye optical illusion
Posted by mathfail
on August 5, 2010
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What’s wrong with that? 5^2-4^2=25-16=9.
At most, the artist could be faulted for not putting a dot in the inner circle. The blue circle has a radius of 3 (pi*3^2 =9pi). The red circle has a total radius of 5, and is missing a circle with a radius of 4 (pi*5^2-pi*4^2=25pi-16pi=9pi).