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If the common ratio is -4/5 and the sum ...

If the common ratio is `-4/5` and the sum of infinite terms in a G.P is `(80)/9` then find the first term.

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` r = (-4)/(5) and S_(oo) = (a)/(1-r) = (80)/(9)`
` therefore (a)/(1+ (4)/(5)) = (80)/(9)`
` rArr 5a = 80 `
` rArr a = 16`
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