The quickplot feature of mathcad is very convinient but it snot perfect. Normally Mathcad would go through the default abscissa range from -10 to 10 and calculate the ordinate values and scales the ordinate accordingly.
In case of your function this algorithm failed (which it shouldn't and I consider this a bug).
So you can help Mathcad by specifying the endpoint values at the ordinate yourself (see attached sheet). Or alternatively you can change the values at the abscissa (f3(-10) seems to be to large for the quickplot) as Jakov suggested.
If you use range variables, as Jacov has proposed, you have more control over accuracy as you choose the step width yourself. The only disadvantage i Mathcad 15 is, that this variable now has a value (the range) and could not be cleared again for subsquent calculations.
