Explanation

The diagonal of a square is the straight line that connects two opposite corners of the square. The length of the diagonal can be calculated using the Pythagorean theorem.

The formula for the diagonal of a square is: Diagonal = √(2 x (side)^2)

In this case, the side of the square plate is 28 cm.

So the diagonal of the square plate is: Diagonal = √(2 x (28)^2) = √(2 x 784) = √1568 = 39.45 cm

Therefore, the diagonal of the square plate is 39.45 cm