I believe this is a geometric sequence.

Do you mean a_{n }= (-1)^{n }* (n+1) ?

In that case, just plug in n=15.

a_{15} = (-1)^{15} * (15+1) = -1 * 16 = -16

I believe this is a geometric sequence.

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Do you mean a_{n }= (-1)^{n }* (n+1) ?

In that case, just plug in n=15.

a_{15} = (-1)^{15} * (15+1) = -1 * 16 = -16

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## Comments

Yes, thanks so much!!

What about this one?

find the 3rd term in the sequence: a

_{n }=(-1)^{n+1}5^{n+1}a

_{3}= (-1)^{3}^{+1}5^{3+1}= (-1)^{4}5^{4 }= 1*625 = 625Now see if you can compute some other problems with calculating terms in sequences. These two examples should give you the enough of an idea. I assume these are from a textbook. Good Luck!

Thanks! But would it not be -625?