### Home > APCALC > Chapter 7 > Lesson 7.1.5 > Problem 7-48

7-48.

** **Homework Help ✎

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 *r*, because the *r* changes. That is where Calculus comes in...

Implicitly differentiate with respect to time, *t*.