CPM Homework Help : CALC Problem 10-58

Mariah walks toward a wall with a flashlight beaming straight ahead. When she is $5$ feet away, the radius of the circle is $2$ feet. If she walks $0.5$ feet per second, find the rate at which the diameter of the circle of light is changing.

Hint:

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

Step 1:

Differentiate:

More Help:

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