Why is my plot linear when the anonymous function z is clearly nonlinear?

Rt = 10688; v = 18; f = 9; KD = 7.73*10^(-5); Kx = 5.8*10^(-5); L0 = 2*10^(-9);
Req = [6000:12000];

z = @(Req) ((Req.*(1+v.*(L0/KD).*(1+Kx*Req).^(f-1)))/Rt)-1;
figure
plot(Req,z(Req));

Answer 1

[Matt J]

It simply looks linear because you are plotting it over too narrow a range.

Req = 0:120000;
plot(Req,z(Req));

[John D'Errico]

The funny thing is, the range of [6000:12000] probably SEEMS wide. But width is a subjective thing in this case.