# Geometric progression

An infinite geometric progression has a finite sum. Given that the sum of the first two terms is 9 and the third term is 12.

1/ Find the value of the first term and the common ration r.

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thrill3rnit3
Gold Member
Work shown?

Work shown?
what???? i cannot really understand what you r saying
i just need help..lolzz...in fact don't really know where to start..y the way i know the equation

thrill3rnit3
Gold Member
what???? i cannot really understand what you r saying
i just need help..lolzz...in fact don't really know where to start..y the way i know the equation
Well, I can't just spoonfeed you with the answer.

A geometric progression can be written as a, ar, ar2, ar3,..., arn

Where a is the first term, and r is the common ratio

If the sum of the first two terms is 9, we can rewrite that as

a + ar = 9

If the third term is 12, we can rewrite it as

ar2 = 12

Now you have 2 equations in 2 unknowns. I think it should be solvable now.