TI-89/series stuff

Test Preparation AP Test Preparation
1

<p>Why is it that sometimes when I enter a series, the 89 will give me the sum, but sometimes it just gives me back the sum?</p>

<p>For example, if I enter SIGMA(1/((2*x)!),x,0,5) then I get the sum, but if I enter</p>

<p>SIGMA(1/((2*x)!),x,0,INFINITY) (actually putting in the infinity symbol of course)</p>

<p>then it just gives it back to me in sigma notation. What am I doing wrong?</p>

2

<p>It might actually be trying to evaluate it for every value since it can not find a closed form for it. It will never reach infinity. Just enter a large number. For that one even like 20 will be fine because 40! is huge.
Or you could have your mode on exact and not approx, but Ive never used sigma before so Im not sure.</p>

3

<p>Oh, ok. Thanks.</p>