What is the perimeter of a square whose diagonal is 3 radical 2

Use trigonometry to get the side of the square. The diagonal of a square creates two right triangles. These right triangles are consistent - meaning their angles have 90, 45 and 45 degrees.
Getting the length of the side can either be used a cosine or sine function, that is
cos 45 = (3 radical 2)/x
x = (3 radical 2)/cos 45
x = 6

The perimeter of the square is 4*sides. Therefore,
P = 4*6 = 24 cm