Evaluating Expressions on the 9970G

On the 9970, in the algebraic mode there is no decent way of evaluating an expression. The approx command will evaluate an expression using the values of all variables, but you can only assign values to variables in Run mode, and if you go back to run mode to assign a value then you lose the expression, and have to type it in again, assuming you remember what it was. So if you want to evaluate an expression for several different values you'd have to go back and forward from run mode and algebraic mode typing the expression in each time.

But you can use a special trick to evaluate certain expressions.
1) suppose you've typed in an expression or generated one by some calculation. Then this expression will be in 'Ans' memory.
2) Since differentials can be evaluated then integrate an expression and then differentiate it and evaluate.
example: to evaluate the expression X^7+2X^3+1 at X=2 then type the expression in and press 'EXE' then type in the following:
diff(integral(Ans),X,1,2) and press 'EXE'. (Where integral is the integral symbol. The 1 refers to first order differentiation.)
To evaluate it at a different value, then press 'AC/on' and then use the up arrow to scroll back to the typed in expression or calculation that generated the expression. Then press 'EXE' to get this expression into 'Ans' memory again, and use the diff method again. Of course all the above would be unnecessary if the algebraic features weren't coseted away in their own mode, inaccessible to the rest of the calculator.