How do I find the first term of a geometric sequence?

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Answer 1 · 2015-11-15T14:55:41

In geometric sequences there is a case of repeated multiplication

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#a,ar,ar^2.....,ar^(n-1#
#----n----#

So the sum of the first n terms of sequence is ;

#S_n =( a(1-r^n))/(1-r)#

Now given you know r n and the sum you find a by re arranging

Additionally

If you re given the nth term then'

#a_n = ar^(n-1)#

You may often has to use both these equation to get to the answer