Arithmetic and Geometric Sequences.

Jul 2015
559
14
United States
Hi, I just did these problems for my final review. Does anyone mind checking them? Tyvm.

1) Find the 98th term of an arithmetic sequence whose first three terms are 2,6,10
Ans: 390

2)Write the 21st term in arithmetic sequence with a first term of 7, and a common difference of 5.
Ans: 107

3) Find the sum of the first term of the first six terms of the geometric sequence, 8,4,2. . .
Ans: 63/4

4) Insert two Geometric means between 4 and 256.
Ans: 16, 64

5) Find the eight term of a geometric sequence whose first three terms are 9,3, and 1.
Ans: 1/243

6)Find the sum of the first 30 terms of the arithmetic sequence 5,8,11. . .
Ans: 240
( I think I did number 6 wrong).
 

romsek

MHF Helper
Nov 2013
6,639
2,989
California
Hi, I just did these problems for my final review. Does anyone mind checking them? Tyvm.

1) Find the 98th term of an arithmetic sequence whose first three terms are 2,6,10
Ans: 390
correct

2)Write the 21st term in arithmetic sequence with a first term of 7, and a common difference of 5.
Ans: 107
correct

3) Find the sum of the first term of the first six terms of the geometric sequence, 8,4,2. . .
Ans: 63/4
correct

4) Insert two Geometric means between 4 and 256.
Ans: 16, 64
correct

5) Find the eight term of a geometric sequence whose first three terms are 9,3, and 1.
Ans: 1/243
correct

6)Find the sum of the first 30 terms of the arithmetic sequence 5,8,11. . .
Ans: 240
( I think I did number 6 wrong).
$a_n=5+3n$

$\displaystyle{\sum_{n=0}^{29}}5+3n = 30\cdot 5 + 3\dfrac{29\cdot 30}{2} = 1455$
 
Nov 2009
717
133
Wahiawa, Hawaii
If you by chance have a TI-Nspire CX CAS
seq(2+4(n-1),n,98,98)
This returns {390}