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\(\int x(1-x)^{10}dx =\)

  • A.\(\frac{(1-x)^{12}}{12} - \frac{(1-x)^{11}}{11} + C\)
  • B.\(\frac{(1-x)^{12}}{12} + \frac{(1-x)^{11}}{11} + C\)
  • C.\(\frac{(1-x)^{11}}{11} - \frac{(1-x)^{10}}{10} + C\)
  • D.\(\frac{(1-x)^{12}}{12} + \frac{(1+x)^{11}}{11} + C\)
  • E.\(\frac{(1-x)^{12}}{12} - \frac{(1+x)^{11}}{11} + C\)

Answer: A

The integral is \(\frac{(1 - x)^{12}}{12} - \frac{(1 - x)^{11}}{11} + C\).

Substitute \(u = 1 - x\), so \(x = 1 - u\) and \(dx = -du\):

\[ \begin{aligned} \int x(1 - x)^{10}dx &= -\int (1 - u)u^{10}du \\ &= \int (u^{11} - u^{10})du \\ &= \frac{u^{12}}{12} - \frac{u^{11}}{11} + C \end{aligned} \]

Putting back \(u = 1 - x\) gives the answer. The '+' version comes from losing the minus sign of dx, and the options with \((1 + x)^{11}\) use the wrong substitution.

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