Xxyy=zz*zz, so the value of y is one of (1, 4,5,6,9). When 1 is taken, z is (1 or 9), and the result is invalid. When 4 is taken, Z is (2 or 8), 8 holds, x = 7, y = 4, and z = 8.

By the way, z is greater than 2 because the square of 2 digits is 4 digits.