Find the side of a square whose diagonal is of the given measure. given = 15 square root 2

  15 units .

In this case, a square, the two sides of the square (forming a right triangle) are equal), and the "diagonal" forming is the hypotenuse of the right triangle.

In these cases, the measurements of the angles of the right triangle are "45, 45, 90" ; and the measurements of the sides are:  "a, a, a√2" ; in which "a√2" is the hypotenuse.

We are given:  "15√2" is the hypotenuse" ; and we are given that this is a right triangle of a square with a diagonal length (i.e. "hypotenuse" of "15√2" ; so the measure of the side of the "square" (and other two sides of the triangle formed) is:  15 units.   (i.e.,  15, 15, 15√2 ).