The radius r (cm) of a circle is related

to time t (seconds) by the equation

r=0.4t + 1.5.

(a) Calculate the initial value of the

radius.

(b) Find the rate of change of r.

a) 1.5cm

b) dr/dt = 0.4cm/sec

Step-by-step explanation:

r = 0.4t + 1.5

Initial is at t = 0,

r = 1.5 cm

b)

dr/dt = 0.4cm/sec

Slope = change in r/change in t

0.4 is the rate of change in r with respect to time

Alternately,

At t = 0, r = 1.5

At t = 1, r = (0.4) (1) + 1.5 = 1.9

(1.9-1.5) / (1-0) = change in r/change in time

= 0.4 cm/sec