SOLUTION: I'm doing series and sequences, and I'm having an issue with this problem: "Write the next term in the sequence. Then write a rule for the nth term." -5, 10, -15, 20,... I

Algebra ->  Sequences-and-series -> SOLUTION: I'm doing series and sequences, and I'm having an issue with this problem: "Write the next term in the sequence. Then write a rule for the nth term." -5, 10, -15, 20,... I      Log On


   

Question 295547: I'm doing series and sequences, and I'm having an issue with this problem:
"Write the next term in the sequence. Then write a rule for the nth term."
-5, 10, -15, 20,...
I figured out that the next term in the sequence is -25, but I can't figure out a rule to explain it. We've tried everything that comes to mind, and the problem seems so simple but it feels as though something is just beyond my grasp.
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
Alternating signs with multiples of 5.
To get alternating signs,
+%28-1%29%5E%28n%29+
To get powers of 5,
5%2An
Now put it all together.
an=%28-1%29%5En%2A5%2An
.
.
.Let's check.
a1=%28-1%29%2A5=-5
a2=%28-1%29%5E2%2A5%2A2=10
a3=%28-1%29%5E3%2A5%2A3=-15
.
.
.