### Home > CALC > Chapter 10 > Lesson 10.1.6 > Problem 10-58

10-58.

Mariah walks toward a wall with a flashlight beaming straight ahead. When she is 5 feet away,

The radius is directly proportional to Mariah's distance from the wall. That is, *d* = *kr*.

Differentiate:

The equation uses the radius, but the question asks about the diameter.