We will calculate it like this, We will make a right angle triangle by adding one new point called O for example, and O is located right under the point C, and on the right side of point D, so the coordinated for this point are O (8, -2). From there, length CD is calculated using the Pythagorean theorem, because we know that the CO = 4 and DO = 4, so:
CD^2 = CO^2 + DO^2
CD^2 = 4^2 + 4^2
DC^2 = 16 + 16
DC^2 = 32
DC = square root of 32 = square root of 16 * square root of 2
DC = 4 * square root of 2
The correct answer is B. 4*square root of 2.
