Answer:
Yes then no
Explanation:
A linear function is of the form y=mx+b, where b and m are constants(not variables). Since the input is the radius, we make that x. The circumference is πd, or 2πr, so if we plug in 2π for m, circumference for y, and 0 for b, this works. The area is πr², which would mean that m would have to be πr. Since r is not a constant, this does not work.