The question "how long is the kite?" is not quite clear, i suppose it was asking how far it was from the ground (b) or horizontally (a). I calculated both, I hope this helps
assume the formula is true for n is equal to k prove that result is true for n is equal to k + 1 hence result proves since the thorum is true for n is equal to 1 and n k + 1 is unit through a and
