### Home > CALC > Chapter 7 > Lesson 7.1.5 > Problem 7-51

7-51.

An alien uses mysterious powers to make crop circles in a Nebraska wheat field. If the radius of a crop circle increases at the rate of

Start with the geometric equation of the area within a circle. There is no Calculus involved in this step.

Do NOT substitute a value for , because the

*changes. That is where Calculus comes in...*

Implicitly differentiate with respect to time, .