I'd suggest reading up more on the Symbolic Math toolbox and and figuring out what your problem really is. Which returns NaN indicating that it used extrapolation (see the help/ documentation).ДЄll in all, I can't figure out what you're trying to do or why you're using interpolation. If you want to evaluate the interp2 line, it appears that you have all of the necessary values: interp2(,4,-3) Generally, if you don't see sym/thefuncname listed at the bottom when you get help for a function funcname, then that function doesn't have a version for symbolic math (or you can directly search help sym/funcname). Additionally, as you discovered, interp2 doesn't accept symbolic inputs. Next, your seventh equation isn't even an equation as there's no = anywhere. Indeed, along with your first equation, EM + ICE = FD, you can use them to solve for the fact that EM = -3. You specified in your fifth and sixth equations that FD = 1 and ICE = 4. The last three equations should look pretty silly to you as they provide no information. Returning a numeric solution using eqn sin (x) x2 - 1 > solve (eqn,x) Warning: Unable to solve symbolically. I don't know if your system is just an example, but it can be solved trivially by inspection without the use of solve.

Solve symbolic equation matlab