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Geometric progression

  • Thread starter jinx007
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  • #1
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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.
 

Answers and Replies

  • #2
thrill3rnit3
Gold Member
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Work shown?
 
  • #3
62
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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
 
  • #4
thrill3rnit3
Gold Member
713
1
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.
 

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