Question
Evaluate the following definite integrals:
$\int_{0}^\limits{1}\text{x}(1-\text{x})^5\text{ dx}$

Answer

We have,
$\int_{0}^\limits{1}\text{x}(1-\text{x})^5\text{ dx}$
Expanding $(1 - x)^5$ by Binomial theorem,
$\therefore\ (1-\text{x})^5=1^5+{^5\text{C}_1}(-\text{x})+{^5\text{C}_2}(-\text{x})^2\\+{^5\text{C}_3}(-\text{x})^3+{^5\text{C}_4}(-\text{x})^4+{^5\text{C}_5}(-\text{x})^5$
$=1-5\text{x}+10\text{x}^2-10\text{x}^3+5\text{x}^4-\text{x}^5$
$=\int_{0}^\limits{1}\text{x}(1-5\text{x}+10\text{x}^2-10\text{x}^3+5\text{x}^4-\text{x}^5)\text{dx}$
$=\Big[\frac{\text{x}^2}{2}-\frac{5\text{x}^3}{3}+\frac{10\text{x}^4}{4}-\frac{10\text{x}^5}{5}+\frac{5\text{x}^6}{6}-\frac{\text{x}^7}{7}\Big]^1_0$
$=\frac{1}{2}-\frac{5}{3}+\frac{10}{4}-\frac{10}{5}+\frac{5}{6}-\frac{1}{7}$
$=\frac{1}{42}$

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