First, draw a diagram to show the situation:
Notice that a right triangle is formed. Let h be the height of the flagpole, measured in ft. From the Pythagorean Theorem, we know that:
[tex]h^2+7^2=20^2[/tex]
Solve for h:
[tex]\begin{gathered} \Rightarrow h^2+49=400 \\ \Rightarrow h^2=400-49 \\ \Rightarrow h^2=351 \\ \Rightarrow h=\sqrt[]{351} \\ \Rightarrow h=3\cdot\sqrt[]{39} \\ \Rightarrow h\approx18.735 \end{gathered}[/tex]
Therefore, the height of the flagpole is:
[tex]\begin{gathered} 3\cdot\sqrt[]{39}\text{ ft} \\ \approx18.735\text{ ft} \end{gathered}[/tex]
