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

7-71.

Remember Eric and the *tip* of his shadow moving away from the lamppost? Draw a diagram before you start this problem.

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, .