What is the 8th term of the geometric sequence where a1 = 625 and a3 = 25

well you know that the first term is 625 so find the difference by finding out what 625 +x = 25 then you know the difference. then you plug that into the equations that should have been provided for you

this is virtually identical to your previous question: http://openstudy.com/updates/4fc29732e4b0964abc83e4db use the same methods explained to you there to find the answer.

Again, utilize the formula \(a_n=a_1 C^{n-1}\) to find out what \(C\) is for your sequence.

that formula confuses me

What is confusing you about it? Every time you add \(1\) to \(n\), you are increasing the term by a power of \(C\), which is what you want. \(C\) is the common ratio.

I would then suggest you use this site to first learn a bit more about these types of sequences: http://www.mathsisfun.com/algebra/sequences-sums-geometric.html

try to solve yourself

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