# Thread: TI84 PLUS SUMMATION sequence

1. ## TI84 PLUS SUMMATION sequence

My cal has OS2.53

A seq of no.$\displaystyle X_1,X_2...$ is such that $\displaystyle x_1=1$ and $\displaystyle x_{n+1}=\frac{5}{X_n} +1$

Find the value of N such that $\displaystyle \displaystyle\sum_{n=1}^N X_n$ is less than 60

2. Originally Posted by helloying
My cal has OS2.53

A seq of no.$\displaystyle X_1,X_2...$ is such that $\displaystyle x_1=1$ and $\displaystyle x_{n+1}=\frac{5}{X_n} +1$

Find the value of N such that $\displaystyle \displaystyle\sum_{n=1}^N X_n$ is less than 60
1. I assume that you are looking for the greatest number N such that the sum is less than 60. Right?

2. I didn't find a way to do the necessary calculations in one step, but I had to use 2 steps:

3. Switch the calculator into SEQ-mode.
4. Enter at y=

nMin=1
u(n)=5/(u(n-1))+1

(You'll find the u at 2ND 7)

5. Go to TBLSET

TblStart = 1
$\displaystyle \Delta$Tbl = 1

6. Create the sequence and store it into the list L1:

seq(u(n),n,1,21,1) STO L1

7. Next step

sum(L1)

8. To change the limits of the summation you can recall the last commands by using 2ND ENTER