Casio fx-CG50 field manual for IB Math
Working with sequences
Enter a sequence, open its table, and scroll until the first row where the sequence value is greater than a chosen threshold.
Find the first value of n for which the sequence un=10(1.2)n exceeds 1000.
From the MAIN MENU open Recursion (icon 8). If necessary, press (TYPE), then (an) so the calculator is expecting an explicit sequence. On the an= line, type 10(1.2)^n with , inserting n with (n.an···) . Press .
Press (SET) and set Start to 0 and End to 30. Start carries over from whatever you did last, and the index you read off the table depends on it. End at 30 runs the table far enough to catch the first value above 1000. Then press (TABLE) and scroll down until the sequence first passes 1000.
The first value is n=26, because u25≈954 but u26≈1140.
Your turn
Work each one on your calculator, then check the answer.
- 1
Find the first n for which un=5(1.3)n exceeds 2000.
- 2
Find the first n for which un=4n(1.1)n exceeds 600.
- 3
Find the first n for which un=8(1.25)n exceeds 300.