1.

What is `int(dx)/(2^(x) -1)` equal to ?A. `ln (2^(x) -1) + c`B. `(ln(1 -2^(-x)))/(ln 2) + c`C. `(ln (2^(-x) -1))/(2ln 2) + c`D. `(ln(1 + 2^(-x)))/(ln 2) + c`

Answer» Correct Answer - B
`int (dx)/(2^(x) -1) =int (dx)/((1)/(2^(-x)))`
`= int (2^(-x))/(1 -2^(-x)).dx`
Let `1 - 2^(-x) = t`
`rArr 2^(-x) .log 2 = (dt)/(dx) rArr 2^(-x) = (1)/(log 2).(dt)/(dx) rArr 2^(-x).dx = (dt)/(log 2)`
`:. int (2^(-x))/(1 -2^(-x)) dx = (1)/(log 2) int (dt)/(t) = (1)/(log 2) (log t) + c`
`= (1)/(log2) (log (1 - 2^(-x))) + c`


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