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Integrate the rational function: 1ex-1[Hint: Put ex = t]

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Question

Integrate the rational function:

`1/(e^x -1)`[Hint: Put ex = t]

Sum
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Solution

Let `I = int 1/ (e^x - 1)  dx`

Put ex = t

⇒ ex dx = dt

⇒ `dx = dt/t`

∴ `I = int dt/ (t (t - 1))`

Let `1/ (t (t - 1)) = A/t + B/ (t - 1)`

⇒ 1 = A (t - 1) + Bt                        .....(i)

Putting t = 1 in (i), we get 

B = 1

Putting t = 0 in (i), we get

1 = A (0 - 1) + B (0)

⇒  A = -1

∴ `1/ (t (t - 1)) = (-1)/t + 1/ (t - 1)`

∴ `I = int (-1/t + 1/ (t - 1))  dt`

= - log |t| + log |t - 1| + C

= - log |ex| + log |ex - 1| + C

`= log  ((e^x - 1)/e^x) +C`

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Chapter 7: Integrals - Exercise 7.5 [Page 323]

APPEARS IN

NCERT Mathematics Part 1 and 2 [English] Class 12
Chapter 7 Integrals
Exercise 7.5 | Q 21 | Page 323

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