(without using recursive formula) then use your formula to find the 23rd term.
3,7,11,15,19,23...
2006-10-21 02:56:11 · 4 answers · asked by Daniella M 1 in Science & Mathematics ➔ Mathematics
sofarsogood,
You were very close, but you dropped the negative sign on your final answer. A good way to avoid this is to rearrange the final formula. You had "-1 + 4*x". I would rewrite it as "4*x - 1". Therefore, the 23rd element would be 4*23 - 1 = 91.
2006-10-21 03:44:59 · answer #1 · answered by Dave 6 · 1⤊ 0⤋
Often a good way to start looking for a formula is to look at differences between consecutive members:
7 - 3 = 4
11 - 7 = 4
15 - 11 = 4
19 - 15 = 4
...
Bingo!
So the general term is going to look like t0 + 4*n. Rather than try tom memorize some formula for the first term, just by inspection (assuming the first term is term 1 and not term 0) it is -1 + 4n. Try this out to make sure:
n = 1, -1 + 4 = 3
n = 2, -1 + 8 = 7...
Yes. So the 23rd term is 1 + 23*4 = 93
2006-10-21 03:01:50 · answer #2 · answered by sofarsogood 5 · 2⤊ 1⤋
1st term is 3
2nd term is 1st term + 4
3rd term is 2nd term + 4
Let 1st term be T
2nd term will be T + 4 =
3rd term will be 4 + T + 4 = T + (2)4
nth term will be T + 4(n-1)
23rd term will be 22 (4) +3 = 91
2006-10-21 06:49:30 · answer #3 · answered by kenyanmartin2000 2 · 1⤊ 0⤋
THE FIRST TERM, a=3
THE COMMON DIFFRENCE BETWEEN EACH TERM, d=4
So the 23rd term:
a+(n-1)d
ie. a+(23-1)d
a+22d = 3+(22*4)
3+88=91
2006-10-21 04:37:10 · answer #4 · answered by tut_einstein 2 · 1⤊ 0⤋