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Geometric series ! Help
Hey guys I got stuck on this question:
The sum of the first three terms of a geometric series is 30.5.If the first term is 8,find possible values of R.
So substituting the values in the rule for the sum of a geometric series i got:
30.5 = 8(r^3 - 1 ) / r - 1
30.5(r-1)= 8(r^3 -1)
What do I do next ?
Can I cancel out the (r^3 -1) / (r -1 ) to give me r^2 - 1?
thanks!
The sum of the first three terms of a geometric series is 30.5.If the first term is 8,find possible values of R.
So substituting the values in the rule for the sum of a geometric series i got:
30.5 = 8(r^3 - 1 ) / r - 1
30.5(r-1)= 8(r^3 -1)
What do I do next ?
Can I cancel out the (r^3 -1) / (r -1 ) to give me r^2 - 1?
thanks!
Rather than putting it into the sum formula, you can use what you know to very easily form a quadratic expression,:
8+ar+ar^2 =30.5
8+ar+ar^2 =30.5
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