Chapter 8.4, Problem 30E

The purpose of this project is to calculate the height of a tall building by using similar triangles. Choose a tall building, and measure the length of its shadow. Now have an assistant measure the length of your shadow. The top of the building, the base of the building, and the tip of the shadow of the building form a triangle, say, $\Delta ABC$, Likewise, the top of your head, your heels, and the tip of your shadow form a triangle, say, $\Delta DEF$. (See Figure $8.68$.)

Assuming that rays of sunlight are parallel, we conclude that $\Delta ABC$ and $\Delta DEF$ are similar. Use the ratio of your height to the length of your shadow to calculate the height of the building.