Let n geq 5 be an integer. If 9^{n}-8n-1=64al | vedclass

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(C) We have $9^{n} = (1+8)^{n} = 1 + n(8) + { }^{n}C_{2}(8^{2}) + { }^{n}C_{3}(8^{3}) + \ldots + { }^{n}C_{n}(8^{n})$.So,$9^{n}-8n-1 = { }^{n}C_{2}(8^

Vedclass · Accepted Answer

${ }^{n} C_{3}(8-5)+{ }^{n} C_{4}(8^{2}-5^{2})+\ldots+{ }^{n} C_{n}(8^{n-2}-5^{n-2})$

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(C) We have $9^{n} = (1+8)^{n} = 1 + n(8) + { }^{n}C_{2}(8^{2}) + { }^{n}C_{3}(8^{3}) + \ldots + { }^{n}C_{n}(8^{n})$.So,$9^{n}-8n-1 = { }^{n}C_{2}(8^{2}) + { }^{n}C_{3}(8^{3}) + \ldots + { }^{n}C_{n}(8^{n}) = 64\alpha$.Thus,$\alpha = { }^{n}C_{2} + { }^{n}C_{3}(8) + { }^{n}C_{4}(8^{2}) + \ldots + { }^{n}C_{n}(8^{n-2})$.Similarly,$6^{n} = (1+5)^{n} = 1 + n(5) + { }^{n}C_{2}(5^{2}) + { }^{n}C_{3}(5^{3}) + \ldots + { }^{n}C_{n}(5^{n})$.So,$6^{n}-5n-1 = { }^{n}C_{2}(5^{2}) + { }^{n}C_{3}(5^{3}) + \ldots + { }^{n}C_{n}(5^{n}) = 25\beta$.Thus,$\beta = { }^{n}C_{2} + { }^{n}C_{3}(5) + { }^{n}C_{4}(5^{2}) + \ldots + { }^{n}C_{n}(5^{n-2})$.Subtracting the two expressions:$\alpha - \beta = { }^{n}C_{3}(8-5) + { }^{n}C_{4}(8^{2}-5^{2}) + \ldots + { }^{n}C_{n}(8^{n-2}-5^{n-2})$.This matches option $C$.

Let $n \geq 5$ be an integer. If $9^{n}-8n-1=64\alpha$ and $6^{n}-5n-1=25\beta$,then $\alpha-\beta$ is equal to

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