मराठी
महाराष्ट्र राज्य शिक्षण मंडळएचएससी विज्ञान (सामान्य) इयत्ता ११ वी

Evaluate the following limit : limx→1[x+x2+x3+.........+xn-nx-1]

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प्रश्न

Evaluate the following limit :

`lim_(x -> 1)[(x + x^2 + x^3 + ......... + x^"n" - "n")/(x - 1)]`

बेरीज
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उत्तर

`lim_(x -> 1)[(x + x^2 + x^3 + ......... + x^"n" - "n")/(x - 1)]`

= `lim_(x -> 1)[(x + x^2 + x^3 + .... +  x^"n" - (1 + 1 + 1 + ...  "n times"))/(x - 1)]`

= `lim_(x -> 1) ((x - 1) + (x^2 - 1) + (x^3 - 1) + ... + (x^"n" - 1))/(x - 1)`

= `lim_(x -> 1)[(x^1 - 1^1)/(x - 1) + (x^2 - 1^2)/(x - 1) + (x^3 - 1^3)/(x - 1) + ... +  (x^"n" - 1^"n")/(x - 1)]`

= 1 (1)0 + 2 (1)1 + 3 (1)2 + 4 (1)3 + ... + n (1)n–1  ...`[lim_(x -> "a") (x^"n" - "a"^"n")/(x - "a") = "na"^("n" - 1)]`

= 1 + 2 + 3 + 4 + ... + n

= `("n"("n" + 1))/2`

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पाठ 7: Limits - Exercise 7.1 [पृष्ठ १३९]

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