How to set the third and fourth arguments of root function?

[#1]

Hi Expert,

Here is a piecewise continuos function. I can get the two root by root function. But the third root with an error "The function values on the end points must be of opposite signs." How can I set he third and fourth arguments of root function?

[wayne]

Three options, 1) symbolic,  2) ployroot  3) try finding root of M(x)/M'(x), but I guess root has trouble because the function does not cross the axis.

[bmi]

Hi Wayne,

Thanks for your help.

About the piecewise function, we know M(200)=0. The root x=200 is existing. But the root(f,x,a,b)  should be monotonic function in the neighbourhood of the root value. So we can use ployroot function resolving the special root.

Thanks again.