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2015-12-26T14:05:08+05:30
1) u(4) = 135 Let first term be a , common difference be r . => u(4) = ar^3 = 135 Now : { u(9) / u(4) } = ar^8 / ar^3 = r^5 = 3^5 => r = 3 = common ratio Now : ar^3 = 135 => 27a = 135 => a = 5 = first term . 2) S = a(r^n - 1 ) / ( r - 1 ) => S(10) = 5(3^10 - 1 ) / 2 = a(b - 1) By comparative analysis : 5/2 ( 3^10 - 1 ) = a(b - 1) => a = 5/2 & b = 3^10
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