Question: Plot of ln(cosh(x)) stops unexpectedly

The function I am attempting to plot is:

z(x) = z0 −(v1/g)*ln(cosh(g*x*60/v1))

where z0 is an initial value of 2000 at t=0, g=9.81, v1= 14.9165

my code is then

zx := 2000 - (14.9165/9.81)*ln(cosh(60*9.81*x/14.981))

plot(zx, x = 0..38)

However it seems to stop plotting values after x=19, even though putting values above 19 into zx will return you a numerical answer. Any help on this would be greatly appreciated.

Please Wait...