What is the largest perfect square factor of 40?

The largest perfect square factor of 40 is 4. A perfect square is a number that can be expressed as the product of an integer with itself, such as 4 (2 x 2) or 9 (3 x 3). In the case of 40, the prime factorization is 2 x 2 x 2 x 5. Since the largest perfect square factor must consist of pairs of the same prime factors, the largest perfect square factor of 40 is 2 x 2 = 4.