<p>@WantIvy:</p>
<p>a^2 + b^2 + c^2 + d^2 = 268 –> eqn. 1</p>
<p>ac + bd = 81 –> eqn. 2</p>
<p>To find distance between two points, (a,b) and (c,d), the formula is:</p>
<p>[(a-c)^2+(b-d)^2]^-2
= [a^2 - 2ac+c^2 + b^2 - 2bd + d^2]^-2</p>
<p>So, if you take eqn. 1 and subtract 2xeqn. 2 from it, you would get</p>
<p>a^2 + c^2 + b^2 + d^2 - 2(ac + bd) </p>
<p>which is equivalent in the inside of the distance formula, [a^2 - 2ac+c^2 + b^2 - 2bd + d^2]^-2</p>