# plotting a symbolic function

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mogin jerry on 20 Oct 2020
Commented: Rik on 21 Oct 2020
This question was flagged by Walter Roberson
i need to create symbolic function f(x) equalling ((3*x-5)/(x-3))
then make symbolic equation, invEqn, by setting x equal to f(y).
solve function to solve invEqn for y and use expression to define the symbolic function finv(x)
Plot f and f^-1 on the same axes.using fplot.
can someone write me a code not sure where to start

#### 1 Comment

Rik on 21 Oct 2020
Question posted by mogin jerry restored from Google cache.
If you want to cheat on your homework you shouldn't use a public forum to do it.

Cris LaPierre on 20 Oct 2020
Edited: Cris LaPierre on 20 Oct 2020
Sounds like a homework assignment, so I won't provide an answer, but take a look at the fplot function documentation page. One of the examples on that page can be used to get your started on your assignment.

Walter Roberson on 20 Oct 2020
The first parameter to fplot() must be a symbolic expression or symbolic function or function handle.
The second parameter to fplot() must be the range to plot over.
invEqn = x == f(x);
No,
invEqn = y == f(x);
which you need to solve for x, and the result needs to be a function of y, not a function of x (watch out for what you assign the output to!)
Note: it happens that for functions of the form (A*X-B)/(x-A) that the solution is x = (A*Y-B)/(Y-A) -- just replacing the X with Y. If you plot over the same range, you are not going to be able to tell the functions apart.
This is not something that happens in general, only for that special form. If it were (A*X-B)/(x-C) then the solution would be (C*Y-B)/(Y-A) with the constant having moved from the denominator to the numerator... but your constants are the same between numerator and denominator.
Rik on 21 Oct 2020
Deleted comment:
done this so far:
syms y x f(x) finv(x)
f(x) = ((3*x-5)/(x-3)) ;
Eqn = f(x)==((3*x-5)/(x-3));
invEqn = x == f(x);
finv(x)=invEqn;
fplot(x,f(x))
fplot(x,finv(x))
but its not plotting the graphs opens a blank graph and keeps giving me errors