Identify a1 and r for the sum of the geometric series. −4, 8, −16, 32,…

A₁ is very clear, just the first term, namely -4.now, "r" or the common ratio, for a geometric serie/sequence, you can always tease it out by simply getting the quotient of the "next term by the previous term", in this case, say 8/(-4), or (-16)/8 and so on.recall that a geometric sequence is done by using the common ratio to get the next term, thus the quotient of both terms is, yes, you guessed it, is "r", the common ratio.

The graph isn’t that clear