# Math Help - sequences

1. ## sequences

I was given this question and don't really know where to start, any help would be much appreciated..

"If the sequence a is arithmetic, and a_3 = 5, and a_5 = 15, find a_9"

Is the awnser 35?

2. Originally Posted by 14041471
I was given this question and don't really know where to start, any help would be much appreciated..

"If the sequence a is arithmetic, and a_3 = 5, and a_5 = 15, find a_9"

Is the awnser 35?
Yes

3. Originally Posted by 14041471
"If the sequence a is arithmetic, and a_3 = 5, and a_5 = 15, find a_9"
If the sequence is arithmetic, then the same amount "d" is added at each stage. Then a_4 = 5 + d and a_5 = a_4 + d = (5 + d) + d = 5 + 2d = 15. Then 2d = 10, so d = 5.

Originally Posted by 14041471
Is the awnser 35?
Yup!