1.

`(1)/((1-x)(3-x))`के प्रसार में `x^(n)` का गुणांक होगाA. `(3^(n+1)-1)/(2.3^(n+1))`B. `(3^(n+1)-2)/(3^(n+1))`C. `(3^(n+1)-2)/(3^(n+1))`D. इनमें से कोई नहीं

Answer» Correct Answer - A
`(1)/((1-x)(3-x))=(1)/(2)((1)/(1-x)-(1)/(3-x))`
`=(1)/(2)[(1-x)^(-1)-(3-x)^(-1)]`
`=1/2 [(1-x)^(-1)-1/3(1-(x)/(3))^(-1)]`
`=1/2[(1+x+x^(2)+x^(3)+...)-1/3(1+x/3+(x/3)^(2)+(x/3)^(3)+...)]`
अतः `x^(n)` का गुणांक
`=1/2[1(1)/(3).(1)/(3^(n))]=(1)/(2)((3^(n+1)-1))/(3^(n+1))`


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