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What is `int (e^(x) + 1)^(-1) dx` equal to?A. `ln (e^(x) + 1) + c`B. `ln (e^(-x) + 1) + c`C. `-l (e^(-x) + 1) + c`D. `-(e^(x) + 1) + c` |
Answer» Correct Answer - C Let I `= int (e^(x) + 1)^(-1) dx = int (1)/(e^(x) + 1) dx = int (e^(-x))/(1 + e^(-x)) dx` Let `1 + ^(-x) =t rArr -e^(-x) dx = dt` `:. I = - int (1)/(t) dt = - log t + c = - log (1 + e^(-x)) + c` |
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