# Evaluating a primitive at boundaries: preval

### 5.12.23 Evaluating a primitive at boundaries: preval

The preval command evaluates an expression from one value to another, such as in done when evaluating a definite integral using the Fundamental Theorem of Calculus.

- preval takes three arguments:
  - F, an expression depending on the variable x.
  - a and b, two expressions.
- preval(F,a,b) returns F|x=b−F|x=a.

preval is used to compute a definite integral when the primitive F of the integrand f is known. Assume, for example, that F:=int(f,x), then preval(F,a,b) is equivalent to int(f,x,a,b), but does not require you to recompute F from f if you change the values of a or b.

#### Example.

Input:

preval(x^2+x,2,3)

Output:

6