Define the equality.
Add a constant (16) to each side.
Express the equality as a binomial.
Take the square root of each side.
Add a constant (4) to each side.
This is somewhat different from the Proof that 4 = 3 and the Proof that -1 is a positive number.
Found at Futility Closet, which is where the others came from; it's a wonderful resource for those interested in mathematical playfulness and humor.