Integrate: \(\rm \int \log x \ dx\).

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Airforce Group X MBT 14-Jul-2021 Shift 1
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  1. x (log x + 1) + C
  2. log x - x + C
  3. \(\rm \frac1x\) + C
  4. x (log x - 1) + C

Answer (Detailed Solution Below)

Option 4 : x (log x - 1) + C
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Detailed Solution

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Concept:

Integration by Parts:

∫ f(x) g(x) dx = f(x) ∫ g(x) dx - ∫ [f'(x) ∫ g(x) dx] dx.

Definite Integral:

If ∫ f(x) dx = g(x) + C, then \(\rm \int_a^b f(x)\ dx = [ g(x)]_a^b\) = g(b) - g(a).

Calculation:

Let I = ∫ (1)(log x) dx.

Considering log x as the first function and 1 as the second function, we get:

= (log x) ∫ 1 dx - ∫ [\(\rm\frac1x\) ∫ 1 dx] dx

= (log x) x - x + C

= x (log x - 1) + C

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