I think if you square a number then take the original number off you will always get an even number. For example: say your chosen number was six= ...... 6x6=36 ...... 36-6=30 ...... and 30 is an even number.
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You can also do it with odd numbers. For example:11x11=121 121-11=110 so that works to.
But no one said you can only do integers so lets try some decimals:9.4x9.4=88.36
88.36-9.4=78.96 so that works to. So I think my theory is correct that the answer will be even when you when you square a number and take your original number away.