Which function increases at a faster rate on 0 to infinity, f(x)=x2 or g(x)=2x

For the domain x<=0:

f(x) = x^2 will increase at a faster rate because the rate of change of gradient is increasing, by contrast for the function:
g(x) = 2x, the rate of change of gradient is 0 (always remains at 2).

Therefore f(x) = x^2 increases at a faster rate.

Im pretty sure it would be 6 purple rectangles.

The answer that i got was 8/3