Numerical Integration
Press 
to access the numerical integration option
which approximates the definite integral
of an expression with respect to a variable from a start value to an end value.
Next, enter an expression, the variable, a start value, and an end value
separated by commas. For example, to find the antiderivative of x3
evaluated from x = 1 to x = 2, enter
3 
1 2
Note: For more specific information and tips see
Integration on the
TI-how does it work?.