# Integrals on TI-85

• Aug 3rd 2010, 08:41 AM
Chokfull
Integrals on TI-85
I am learning about integrals right now but my book only gave me a short paragraph about the calculator saying "On a TI use the Is> command". I look through the calculator and find that command but don't know what to input after it. Sadly, I don't know where my manual is. (Crying) Anyone know what I should do?

Also, if anyone has the cheat codes for the TI-85 that would be helpful. I could use infinite ammo.
• Aug 3rd 2010, 08:46 AM
Ackbeet
• Aug 3rd 2010, 08:50 AM
Ackbeet
On the TI-85 (which is the same great calculator I have - I still think it's the best one TI has ever put out, with the possible exception of the TI-86), you'd do 2nd - CALC - fnInt - function - , - variable name - , - lower limit - , - upper limit - ) - ENTER.

You want to see this, for example:

fnInt(x^2,x,0,1), then press ENTER. The result is

.333333333333

Does that help?
• Aug 3rd 2010, 10:18 AM
Chokfull
Yes that helps a lot thank you.

I'm still new to integrals, though, so do the "lower limit" and the "upper limit" mean how far to the left and right it extends, respectively?
• Aug 3rd 2010, 10:21 AM
Ackbeet
Right. The TI-85's fnInt(x^2,x,0,1) notation is numerically equivalent to

$\displaystyle \displaystyle{\int_{0}^{1}x^{2}\,dx.}$
• Aug 9th 2010, 10:59 AM
Chokfull
Is there a way to specify for n? It keeps assuming $\displaystyle \displaystyle{\lim _{n \to \infty }$.
• Aug 9th 2010, 11:28 AM
Ackbeet
To what are you referring? Are you trying to do a trapezoidal or Simpson's Rule, without letting the number of partitions go to infinity? fnInt is going to try to compute an accurate numerical integral of your function. If you want to do a finite Riemann-type sum, use the sum seq command:

2nd - MATH - MISC - sum - seq - etc. (look this up in the manual for the exact syntax).

Is that what you're after?
• Aug 9th 2010, 11:43 AM
Chokfull
yeah I think so thanks
• Aug 9th 2010, 11:48 AM
Ackbeet
No problem. Have a good one!