This is the concept of geometry, to get the expression for horizontal distance h as a function of d, we shall use the Pythagorean theorem; c^2=a^2+b^2 thus; hypotenuse=d horizontal=h slanting=8600 thus; d^2=h^2+(8600)^2 This implies that: d=sqrt(h^2+(8600)^2) thus; d(h)=sqrt(h^2+(8600)^2)