pr.probability – What is the probability that penny will fall entirely inside a square?

Question : A player tosses a penny from a distance onto the surface of a square table ruled in 1 in. squares. If the penny is 3/4 in. in diameter, what is the probability that it will fall entirely inside a square (assuming that the penny lands on the table).


Can some help me understand why is the answer (1-2r)**2? Thanks in advance.