Casio fx-9860GII User Manual

Using a graphic display calculator
© Oxford University Press 2012: this may be reproduced for class use solely for the purchaser’s institute
Casio fx-9860GII
Example 26
How many terms of the series
21
1
3
8
9
16
27
++++...
are needed before their sum exceeds 5.5?
In the example u
1
= 2,
r =
2
3
and n is to be found.
S
n
k
k
n
=
⎛
⎝
⎜
⎞
⎠
⎟
−
=
∑
2
2
3
1
1
⋅
The best way to view a table of the sums of a series is in recursive mode.
Press
MENU
. You will see the dialog box as shown on the right.
Choose 8: RECUR and press
EXE
.
Press
F3
TYPE and choose
F2
a n+1 = Aa n + Bn + C
Press
EXIT
Choose a
n+1
and press
F5
SET
Enter the Start value of the table as 1 and the End value as 10
(this is an estimate of how many terms you will need)
Choose a
1
as the fi rst term and enter 2 as the value of a
1
.
Press
EXIT
The recursive formula of a geometric series is u
n+1
= r · u
n
Enter this formula using a
n+1
as
2
3
× a
n
Type
2
3
×
Press
F4
n, a
n
·· and choose
F2
a
n
Press
EXE
Press
SHIF T
SET UP
Select Σ Display and press
F1
On
This will show the cumulative sums of the terms in the table.
Press
EXIT
and then
F6
TABL
The table shows the fi rst four values of the series and its cumulative sums.
The fi rst row show a
1
and a
1
and the second row shows a
2
and a
1
+ a
2
, etc.
Scrolling down the table shows that when n =7, S
n
> 5.5 as required.
26

Casio fx-9860GII Specifications

General

Type	Graphing
Form factor	Desktop
Control type	Buttons
Product color	Silver
Housing material	Plastic
Built-in capability	Yes
Digits	- digits
Display type	LCD
Second display	No
Display tilting	-
Display resolution	64 x 128 pixels
Display character size	8 x 21 mm
Display number of lines	8 lines
Display number of characters	21
Flash memory	1.5 MB
RAM capacity	0.064 MB
Storage media type	Flash
Battery type	AAA
Power source	Battery
Number of batteries supported	4