For me MathStudio is a 5 stars app. Great work!

I got two requests.

In algebra when numerator is greater than denominator we often write down a mixed fraction eg.
11/4 = 2 3/4
Functions that operate with this kind of fractions are missing. Also the input method would be necessary. I suggest three text input fields appropriately aligned.

The second request is about the pane above the virtual keyboard. Often one expression is "in work" within several steps. An answer that comes out from program (let's say after you hit SOLVE) should be involved in next input. I know that clipboard is one solution, but it is clumsy. I suggest tap-and-drag. The answer is tapped and dragged to the next input line or somewhere else.

Also tapping on expression in input line could bring up a context menu: with "copy to new input line" and common (or expected) functions depending on the type of expression.

For implementing this request an intuitive approach could be used. Tapping on non-empty input or output line would select an expression and bring up context menu. If you don't choose from menu, you could simply drag selected item to new empty line or inserted it in an existent expression.

Regards.

Richard