Find the diagonal of a square whose sides are of the given measure.

7 square root of 3

I encourage you to draw in the diagonal. The diagonal of a square will create a triangle with the sides of the square. Specifically, this is a right triangle as the angles of a square are right angles by definition.

Use the Pythagorean theorem: a^2 + b^2 = c^2. In this case, sides a and b are each 7sqrt (3), and c is the diagonal of the square.

a^2 + b^2 = c^2

(7sqrt3) ^2 + (7sqrt3) ^2 = c^2

294 = c^2

c = sqrt (294) = 7sqrt (6)