Skip to main contentSkip to solution

∫dxxn+1−x dx\int \frac{dx}{x^{n+1} - x}\,dx

Solution

✅ Correct Option: 1

Note: The π\pi in the original question is a typo — the integral is ∫dxxn+1−x\int \dfrac{dx}{x^{n+1} - x}.


Factor xx out of the denominator:

xn+1−x=x(xn−1)x^{n+1} - x = x(x^n - 1)

So the integral becomes:

∫dxx(xn−1)\int \dfrac{dx}{x(x^n - 1)}


Divide both the numerator and denominator by xn+1x^{n+1} (i.e., multiply by x−n−1x−n−1\dfrac{x^{-n-1}}{x^{-n-1}}):

Denominator: x(xn−1)⋅x−n−1=x−n(xn−1)=1−x−nx(x^n - 1) \cdot x^{-n-1} = x^{-n}(x^n - 1) = 1 - x^{-n}

Numerator: 1⋅x−n−1=x−n−11 \cdot x^{-n-1} = x^{-n-1}

So we get:

∫x−n−11−x−n dx\int \dfrac{x^{-n-1}}{1 - x^{-n}}\,dx

We do this because the derivative of the denominator will match the numerator — setting up a clean substitution.


Let u=1−x−nu = 1 - x^{-n}

du=n x−n−1 dxdu = n\,x^{-n-1}\,dx

x−n−1 dx=dunx^{-n-1}\,dx = \dfrac{du}{n}

Substituting into the integral:

∫1u⋅dun\int \dfrac{1}{u} \cdot \dfrac{du}{n}

=1n∫duu= \dfrac{1}{n} \int \dfrac{du}{u}

=1nln⁡∣u∣+C= \dfrac{1}{n} \ln|u| + C


Replace uu with 1−x−n1 - x^{-n}:

=1nln⁡∣1−x−n∣+C= \dfrac{1}{n} \ln|1 - x^{-n}| + C

Since 1−x−n=1−1xn=xn−1xn1 - x^{-n} = 1 - \dfrac{1}{x^n} = \dfrac{x^n - 1}{x^n}, we can write:

∫dxxn+1−x=1nln⁡∣xn−1xn∣+C\int \dfrac{dx}{x^{n+1} - x} = \dfrac{1}{n} \ln\left|\dfrac{x^n - 1}{x^n}\right| + C

Keyboard Shortcuts

  • Left arrow: Previous question
  • Right arrow: Next question
  • S key: Jump to solution
  • Q key: Jump to question