Due north and due east have a 90 degree angle between them and they are both 18miles long so if we draw these two sides and join the start and finish ends of these two equal sides, we get a right angle triangle, with the one 90 degree angle and two 45 degree angles (by construction). Taking one 45 degree angle, and making the 18 miles the opposite side, and the hypotenuse or unknown long side as H then the cosine of the 45 degree angle is opposite/hypotenuse or O/H. So we say cos45=O/H and solving for H, then, H =O/cos45 = 18/071=25, so 25 is the answer.
