The fnInt( Command

Approximately computes a definite integral.

fnInt(*f*(*var*),*var*,*a*,*b*[,*tol*])

Press

- Press MATH to access the math menu.
- 9 to select fnInt(, or use arrows.

TI-83/84/+/SE

1 byte

fnInt(*f*(*var*),*var*,*a*,*b*[,*tol*]) computes an approximation to the definite integral of *f* with respect to *var* from *a* to *b*. *tol* controls the accuracy of the integral computed. The default value of *tol* is 10^{-5}. fnInt( returns exact results for functions that are polynomials of small degree.

fnInt( only works for real numbers and expressions. The Gauss-Kronrod method is used for approximating the integral.

**Tip**: Sometimes, to get an answer of acceptable accuracy out of fnInt(, substitution of variables and analytic manipulation may be needed.

```
fnInt(1/X,X,1,2)
.6931471806
fnInt(ln(X),X,0,1) <a difficult example>
-.999998347
fnInt(ln(X),X,0,1,e-11)
-1
```

# Error Conditions

**ERR:DOMAIN**is thrown if*tol*is 0.**ERR:ILLEGAL NEST**is thrown if fnInt( occurs in the expression to be integrated.**ERR:TOL NOT MET**may occur if the tolerance is too small.

# Related Commands

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