Question 1108733
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You should be able to see your mistake if you look at the work you did.  Or maybe it would be better to start over on the problem.  Often if you make a mistake and try to find it by looking at the work you did, you automatically make the same mistake again.<br>
Here is what you show:
a(1) = 1
a(2) = 0
a(3) = a(2)-a(1) = 0-1 = -1  (looks good)
a(4) = a(3)-a(2) = -1-0 = -1  (still looks good)
a(5) = a(4)-a(3) = -1-(-1) = 2  (how about that one -- does it still look good to you?)