Since it is a square, the diagonals are congruent. If a square is split like this, it becomes two congruent right triangles. The relationship between the sides and hypotenuse is a 1:
ratio. So if the diagonal of a square is 14 cm, then the side length would be 14/, which is approximately 9.899. I don't understand what the answer choices are, but you should be able to square root the numbers to determine the answer.