
Here, h is the height of the tree.
from the Pythagorean theorem:
h2 + 802 = (11 + 2h)2
h2 + 6400 = (11 + 2h)(11 + 2h)
h2 + 6400 = 121 + 44h + 4h2 Subtract h2 and 6400 from both sides.
0 = -6279 + 44h + 3h2 Rearrange.
0 = 3h2 + 44h - 6279 Use quadratic formula to solve for h.
\(h = {-44 \pm \sqrt{44^2-4(3)(-6279)} \over 2(3)} \\~\\ h = \frac{-44\pm278}{6} \\~\\ h=\frac{-44+278}{6}=39 \qquad\text{or}\qquad h=\frac{-44-278}{6}=-\frac{161}3\)
So...the height of the tree must be 39 feet