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If limx→1x4-1x-1=limx→kx3-l3x2-k2, then find the value of k.

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Question

If `lim_(x -> 1) (x^4 - 1)/(x - 1) = lim_(x -> k) (x^3 - l^3)/(x^2 - k^2)`, then find the value of k.

Sum
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Solution

Given that `lim_(x -> 1) (x^4 - 1)/(x - 1) = lim_(x -> k) (x^3 - l^3)/(x^2 - k^2)`

⇒ `4(1)^(4 - 1) =  lim_(x -> k) ((x - k)(x^2 + k^2 + kx))/((x - k)(x + k))`

⇒ 4 = `lim_(x -> k) (x^2 + k^2 + kx)/(x + k)`

⇒ 4 = `(k^2 + k^2 + k^2)/(2k)`

⇒ 4 = `(3k^2)/(2k)`

⇒ 4 = `3/2 k`

⇒ k = `8/3`

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Chapter 13: Limits and Derivatives - Exercise [Page 240]

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NCERT Exemplar Mathematics Exemplar [English] Class 11
Chapter 13 Limits and Derivatives
Exercise | Q 28 | Page 240

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