Question 51300
You have two right triangles, in which the two poles are the vertical legs of the triangles, and the length of the wire is the sum of the two hypotenuses (or would that be hypotenii???).  Since the distance between the poles is 30 meters, let x= distance from first pole to the point where the wire touches the ground, and 30-x = distance from this point on the ground to the base of the second pole.


By Theorem of Pythagoras, the length of the wire from the top of the first pole to the ground is {{{sqrt(12^2+x^2) }}}, and the distance from the top of the second pole to the ground is {{{sqrt(21^2 + (30-x)^2) }}}.  The total length of the wire, is the sum of these radicals

{{{sqrt(144+x^2) + sqrt(441+900-60x+x^2) }}} 


It doesn't simplify much:  {{{sqrt(144+x^2) + sqrt(1341-60x+x^2) }}} 


R^2 at SCC