### Home > CALC > Chapter 7 > Lesson 7.2.2 > Problem 7-71

7-71.

Remember Eric and the 16-foot tall lamppost? If Eric (who is 5 feet tall) walks away from the pole at a rate of 4*tip* of his shadow moving away from the lamppost? Draw a diagram before you start this problem. Homework Help ✎

Find similar triangles and write a geometric equation relating their proportional sides.

Use implicit differentiation to convert the geometric equation into a rate equation.

In other words, find the derivative of everything in terms of time, *t*.