# Math Help - Arithmetic Sequence

1. ## Arithmetic Sequence

Hey guys, just a bit of help please.

The first term of an arithmetic sequence is a. The mth term is zero. Find the rule for tn for the sequence.

so far i got

a=a+d(n-1)
0=a+d(m-1)

Subtract:

a=d(n-1)-d(m-1)
...
d=a/(n-m)

so the rule i would write: t_n=a+a/(n-m)

but this isn't right - can anyone see where i went wrong?

2. Originally Posted by qwertyuiop
Hey guys, just a bit of help please.

The first term of an arithmetic sequence is a. The mth term is zero. Find the rule for tn for the sequence.

so far i got

a=a+d(n-1)
0=a+d(m-1)

Subtract:

a=d(n-1)-d(m-1)
...
d=a/(n-m)

so the rule i would write: t_n=a+a/(n-m)

but this isn't right - can anyone see where i went wrong?
I think there is some confusion in your notation because it's really the nth term a_n = a + (n-1)d. a simply equals a. At some point in your calculations, the two were mixed up and treated as a single variable. Your working seems fine, just redo the calculations, making careful distinctions between a_n and a.

Another way to do this question is to simply add (md - md) = 0 to your equation for a_n

3. I see I see what i did wrong ! After like 2340928 times!
haha
Thank you so much Gusbob.

4. Originally Posted by qwertyuiop
I see I see what i did wrong ! After like 2340928 times!
If 1 second for each time, then ~27 FULL days !

5. yea totally ! (: