The tree, pole and the ground form a right triangle, right-angled at the junction of the tree and the ground.
The pole forms a hypotenuse, length 15 ft.
Ground is a leg, 9 ft.
We can use Pythagoras theorem to find the height of the tree, namely
[tex]height=\sqrt{15^2-9^2}[/tex]
[tex]=\sqrt{225-81}[/tex]
[tex]=\sqrt{144}[/tex]
[tex]=12[/tex] ft.
The height of the tree is 12 feet.
