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# Geometric Progression Question watch

1. The sum of the first two terms of a geometric progression is 9 and the sum of the first four terms is 45. Calculate the two possible values of the fifth term in the progression.
____________________

Here's what I got (which is apparently wrong):

The sum of the geometric expressions expressed differently because I believed those were the most simple forms

From here I just substituted in the values and got it wrong, the correct answer however is -144 or 48.

Any and all help is much appreciated.
2. (Original post by Retsek)
The sum of the first two terms of a geometric progression is 9 and the sum of the first four terms is 45. Calculate the two possible values of the fifth term in the progression.
____________________

Here's what I got (which is apparently wrong):

The sum of the geometric expressions expressed differently because I believed those were the most simple forms

From here I just substituted in the values and got it wrong, the correct answer however is -144 or 48.

Any and all help is much appreciated.
Note that r^2 + 1 = 5 => r^2 = 4, not r^2 = 6.
3. (Original post by Retsek)
The sum of the first two terms of a geometric progression is 9 and the sum of the first four terms is 45. Calculate the two possible values of the fifth term in the progression.
____________________

Here's what I got (which is apparently wrong):

The sum of the geometric expressions expressed differently because I believed those were the most simple forms

From here I just substituted in the values and got it wrong, the correct answer however is -144 or 48.

Any and all help is much appreciated.
a + ar = 9
a + ar + ar^2 + ar^3 = 45

solve this simultaneously and then can u take on from there?
4. (Original post by Zacken)
Note that r^2 + 1 = 5 => r^2 = 4, not r^2 = 6.
oh. my. god. I've had a long day...
5. (Original post by brainmaster)
a + ar = 9
a + ar + ar^2 + ar^3 = 45

solve this simultaneously and then can u take on from there?
Did you not read the OP...?
6. (Original post by Zacken)
Did you not read the OP...?
what's OP?😅😅😅
7. (Original post by Zacken)
Did you not read the OP...?
He often doesn't.

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