Consider the schematic diagram below,
Here B represents the base of the tree, while C represents the location of robin.
Note that ABC is a right triangle, so the side AB can be calculated using Pythagoras Theorem as,
[tex]\begin{gathered} \text{ Hypotenuse}^2=\text{Base}^2+\text{Height}^2 \\ AC^2=AB^2+BC^2 \\ 41^2=AB^2+9^2 \\ AB^2=41^2-9^2 \\ AB^2=1600 \\ AB^{}=\sqrt[]{1600} \\ AB=40 \end{gathered}[/tex]Thus, the tree is 40 feet tall.
