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For x∈R−{−1,0,1}x \in \mathbb{R} - \{-1,0,1\}, ∫1x−x5dx\int \frac{1}{x - x^5}dx is equal to

Solution

✅ Correct Option: 1

Look at the denominator: x−x5x - x^5

Factor out xx:

x−x5=x(1−x4)x - x^5 = x(1 - x^4)

The integral becomes:

∫1x(1−x4)dx\int \frac{1}{x(1 - x^4)}dx


Using partial fractions:

1x(1−x4)=Ax+f(x)1−x4\frac{1}{x(1-x^4)} = \frac{A}{x} + \frac{f(x)}{1-x^4}

Multiply both sides by x(1−x4)x(1-x^4):

1=A(1−x4)+x⋅f(x)1 = A(1-x^4) + x \cdot f(x)

Put x=0x = 0:

1=A(1)+01 = A(1) + 0

A=1A = 1

Substitute A=1A=1:

1=(1−x4)+x⋅f(x)1 = (1-x^4) + x \cdot f(x)

x⋅f(x)=x4x \cdot f(x) = x^4

f(x)=x3f(x) = x^3

Therefore:

1x(1−x4)=1x+x31−x4\frac{1}{x(1-x^4)} = \frac{1}{x} + \frac{x^3}{1-x^4}


∫1x(1−x4)dx=∫1xdx+∫x31−x4dx\int \frac{1}{x(1-x^4)}dx = \int \frac{1}{x}dx + \int \frac{x^3}{1-x^4}dx

First integral:

∫1xdx=ln⁡∣x∣\int \frac{1}{x}dx = \ln|x|

For the second integral, let u=1−x4u = 1-x^4

Then dudx=−4x3\frac{du}{dx} = -4x^3, so x3dx=−14dux^3dx = -\frac{1}{4}du

∫x31−x4dx=∫1u⋅(−14)du\int \frac{x^3}{1-x^4}dx = \int \frac{1}{u} \cdot \left(-\frac{1}{4}\right)du

=−14ln⁡∣u∣= -\frac{1}{4}\ln|u|

=−14ln⁡∣1−x4∣= -\frac{1}{4}\ln|1-x^4|


∫1x−x5dx=ln⁡∣x∣−14ln⁡∣1−x4∣+c\int \frac{1}{x - x^5}dx = \ln|x| - \frac{1}{4}\ln|1-x^4| + c

=14[4ln⁡∣x∣−ln⁡∣1−x4∣]+c= \frac{1}{4}\left[4\ln|x| - \ln|1-x^4|\right] + c

=14[ln⁡∣x4∣−ln⁡∣1−x4∣]+c= \frac{1}{4}\left[\ln|x^4| - \ln|1-x^4|\right] + c

=14ln⁡∣x41−x4∣+c= \frac{1}{4}\ln\left|\frac{x^4}{1-x^4}\right| + c

Therefore, the answer is:

14log⁡e∣x41−x4∣+c\boxed{\frac{1}{4}\log_e\left|\frac{x^4}{1-x^4}\right| + c}

Note: log⁡e\log_e is the same as ln⁡\ln (natural logarithm)

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