Command Summary	Command Syntax	Calculator Compatibility	Token Size
Approximately computes a definite integral.	fnInt(f(var),var,a,b[,tol])	TI-83/84/+/SE	1 byte

Menu Location

Press
1. Press MATH to access the math menu.
2. 9 to select fnInt(, or use arrows.

The fnInt( Command

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

• fMin(
• fMax(
• nDeriv(

Authors: KG