Which rule will find the nth term of an arithmetic sequence with a rate of increase equal to 1/2 and a6 = 18?

a.) an = 30 + n/2
b.) an= 7+ n/2
c.) an= 15- n/n
d.) an= 15+ n/2

Thank you for your help! ^_^ xoxo

Question

Which rule will find the nth term of an arithmetic sequence with a rate of increase equal to 1/2  and a6 = 18?

a.) an = 30 + n/2
b.) an= 7+ n/2
c.) an= 15- n/n
d.) an= 15+ n/2

Thank you for your help! ^_^ xoxo

zehanz · Answer

Possible first step: set n=6 in these formulas to filter out the wrong ones.

rishavraj · Answer

$$a_n = a_1 + (n - 1)d$$
u r having a_6
find a_1 and plug it in the above equation......
and also the way @ZeHanz  said would be far easy....

anonymous · Answer

how do I put the an on mathway.com? Lol I don't know how! ;-;

zehanz · Answer

Not sure what you mean...

If I set n=6 in the first one, I get: 30 + 6/2 = 30+3=33, so wrong.

Only if two of the formulas give you 18 as an aswer, you have to do extra work (or thinking...)