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Lösung 2.1:2c

Aus Online Mathematik Brückenkurs 2

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K (Lösning 2.1:2c moved to Solution 2.1:2c: Robot: moved page)
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{{NAVCONTENT_START}}
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If we recall that
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<center> [[Image:2_1_2c.gif]] </center>
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<math>\sqrt{x}=x^{{1}/{2}\;}</math>, the integral can be written as
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{{NAVCONTENT_STOP}}
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<math>\begin{align}
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& \int\limits_{4}^{9}{\left( \sqrt{x}-\frac{1}{\sqrt{x}} \right)}\,dx=\int\limits_{4}^{9}{\left( x^{{1}/{2}\;}-\frac{1}{x^{{1}/{2}\;}} \right)}\,dx \\
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& =\int\limits_{4}^{9}{\left( x^{{1}/{2}\;}-x^{{-1}/{2}\;} \right)}\,dx \\
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\end{align}</math>
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This is a standard integral in which the integrand consists of two terms looking like
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<math>x^{n}</math>, where
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<math>n=\frac{1}{2}</math>
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and
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<math>n=-\frac{1}{2}</math>.
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We obtain
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<math>\begin{align}
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& \int\limits_{4}^{9}{\left( x^{{1}/{2}\;}-x^{{-1}/{2}\;} \right)}\,dx=\left[ \frac{x^{\frac{1}{2}+1}}{\frac{1}{2}+1}-\frac{x^{-\frac{1}{2}+1}}{-\frac{1}{2}+1} \right]_{4}^{9} \\
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& =\left[ \frac{x^{1+\frac{1}{2}}}{\frac{3}{2}}-\frac{x^{\frac{1}{2}}}{\frac{1}{2}} \right]_{4}^{9} \\
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& =\left[ \frac{2}{3}x\sqrt{x}-2\sqrt{x} \right]_{4}^{9} \\
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& =\frac{2}{3}\centerdot 9\centerdot \sqrt{9}-2\sqrt{9}-\left( \frac{2}{3}\centerdot 4\centerdot \sqrt{4}-2\sqrt{4} \right) \\
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& =\frac{2}{3}93-2\centerdot 3-\left( \frac{2}{3}\centerdot 4\centerdot 2-2\centerdot 2 \right) \\
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& =18-6-\frac{16}{3}+4=16-\frac{16}{3} \\
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& =\frac{16\centerdot 3-16}{3}=\frac{32}{3} \\
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\end{align}</math>

Version vom 13:14, 17. Okt. 2008

If we recall that x=x12 , the integral can be written as


94x−1xdx=94x12−1x12dx=94x12−x−12dx


This is a standard integral in which the integrand consists of two terms looking like xn, where n=21 and n=−21.

We obtain


94x12−x−12dx=x21+121+1−x−21+1−21+194=23x1+21−21x2194=32xx−2x94=3299−29−3244−24=3293−23−3242−22=18−6−316+4=16−316=3163−16=332

Von „http://wiki.math.se/wikis/2009/bridgecourse2-TU-Berlin/index.php/L%C3%B6sung_2.1:2c“