The area of a square is 200cm^2. how long is the diagonal?

In order to solve this problem, we first need to find the side lengths of the square.  We know that the area of a square is one length squared, so we can set up this equation:

200 = 

We solve this by taking the square root of both sides.



So, one side of the square is 14.14cm.  To finish this problem, we apply the pythagorean theorem.  We can do this by drawing in the diagonal to make a triangle (shown in attachment - the blue part in the second drawing is the section that we use.  Please note that the drawing is not to scale)

The pythagorean theorem is , where c squared is the diagonal of a right triangle.  A squared and b squared are the other two sides.  We can now plug in our numbers.



So, the diagonal length is 20 cm.

The answer would be choice b