## anonymous 2 years ago how do you type the infinity sign on a graphing calculator ?

1. amistre64

1E99

2. anonymous

i just write it out ?

3. anonymous

it says error

4. amistre64

thats calculator for: 1x10^(99)

5. anonymous

which model

6. anonymous

TI - 84 plus

7. amistre64

your comma button has an EE atop it, shift to get it

8. anonymous

oh i see it now , hold up

9. anonymous

Do you have a TI-89? These bad boys have an infinity BUTTON!! :D

10. anonymous

oh no i have a 84 /:

11. hihi67

lol @austinL

12. amistre64

ti84 is the most ill go ... after that they started having to have terabytes for the instruction manuals and i gave up :)

13. anonymous

@amistre64 it says EE but you said it was IE99

14. anonymous

Same thing :)

15. amistre64

it not my fault they cant type lol

16. anonymous

Button likely says EE, but on screen it should say E

17. anonymous

ok lemme try

18. amistre64

the output on the screen is still: one: 1 2nd, , : E 99: 99

19. anonymous

is it a one or an I ?

20. amistre64

they might have done that to distinguish it fromthe alpha E key :/

21. amistre64

an i is not a real numerical value

22. anonymous

"Imaginary"

23. amistre64

i^k is one of 4 values ... why are you needing an infinity?

24. anonymous

Find the sum of the infinite geometric series, if possible. Show steps, if possible. \sum_{{j}={1}}^{\infty}4 \cdot 0.5^{j-1}

25. anonymous

hold up

26. anonymous

$\sum_{{j}={1}}^{\infty}4 \cdot 0.5^{j-1}$

27. amistre64

$\sum_{{j}={1}}^{\infty}4 \cdot 0.5^{j-1}$ $\sum_{{j}={1}}^{\infty}4 \cdot 0.5^{j}~.5^{-1}$ $\frac{4}{.5}\sum_{{j}={1}}^{\infty}0.5^{j}$

28. anonymous

aha now what ? lol

29. amistre64

is .5 less than 1?

30. amistre64

theres a formula for this ....

31. anonymous

yes

32. anonymous

whats the formula ? im sorry my teacher doesnt give me all this info /:

33. amistre64

$\frac{1-r^k}{1-r}$ if r < 1, then the limit as k to infinity is $\frac{1}{1-r}$

34. anonymous

whats r though ? the common ratio ?

35. anonymous

but would it be possible to find the sum ?

36. amistre64

let me rechk my thought tho ... S = r + r^2 + r^3 + ... + r^n -rS = - r^2 - r^3 - ... - r^n - r^(n+1) ----------------------------------- (1-r)S = r + 0 ..........................- r^(n+1) S= r - r^(n+1) ----------- 1 - r

37. amistre64

if r < 1 then that exponented part goes to 0 leaving us: S = r/(1-r) for the sum

38. amistre64

might be better stated the |r| < 1, but why nitpick

39. amistre64

$\frac{4}{.5}\sum_{{j}={1}}^{\infty}0.5^{j}$ $\frac{4}{.5}~\frac{.5}{1-.5}$ $\frac{4}{.5}=8$

40. amistre64
41. anonymous

thanks soooo much !

42. amistre64

youre welcome, as far as i know the ti84 does not have an infinite sum function

43. anonymous

yes im aware haha