Help evaluating integral

[dae]

Be sure to purge(x) before using preval(F(x),a,b).

If x has been assigned a value, F(x) will be evaluated using the current x value, before calculating F(b) - F(a).

preval(x^2+x, 2, 3)
outputs 6
only if x has not been assigned a value

Similarly:
f(x) := x^2+x
preval(f(x), 2, 3)
outputs 6
only if x has not been assigned a value

If for instance, x has the value 1, preval(f(x),2,3) will output 0.

Fortunately, if x is purged, then f(x) will revert to the symbolic expression without having to be re-entered.