Find x-intercepts for polyfit curve

I used polyfit to generate a best fit curve for my data. I now want to extrapolate backwards to the x-intercept for this curve. I used poly2sym to generate the equation for the curve, but I am now a bit stuck.

I have tried using fnzeros but I keep getting the error 'Input not a function' or 'Input not recognized variable'. What format does the expression have to be in for fnzeros to work? Or is there some other way of finding the intercept points?

Thanks Louis

Answer 1

[Matt J]

The x-intercepts of a polynomials are its roots. Just use the ROOTS command on the output of POLYFIT. No need to do any symbolic manipulation.