The area of a circle increases at a rate of 5 cm-/ s. a. How fast is the radius changing when the radius is 1 cm? b. How fast is the radius changing when the circumference is 3 cm? a. Write an equation relating the area of a circle, A, and the radius of the circle, r. (Type an exact answer, using x as needed.) Differentiate both sides of the equation with respect to t. dA dr dt dt (Type an exact answer, using x as needed.) When the radius is 1 cm, the radius is changing at a rate of (Type an exact answer, using x as needed.) b. When the circumference is 3 cm, the radius is changing at a rate of (Type an exact answer, using x as needed.)