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Home  >>  CBSE XII  >>  Math  >>  Integrals
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Prove the following\[\int\limits_{-1}^1x^{17}\cos^4x\;dx=0\]

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Toolbox:
  • (i) If $f(-x)=f(x)$ then it is an odd function
  • (ii) $\int \limits_{-a}^a f(x) =0$ if f(x) is an odd function
Given Prove that $\int \limits_{-1}^1 x^{17} \cos ^4 x dx =0$
 
Given $I= \int \limits_{-1}^1 x^{17} \cos ^4 x dx =0$
 
Let $f(x)=x^17 \cos ^4 x$
 
Therefore $f(-x)=(-x)^{17}\cos ^4 (-x)=-x^{17} \cos ^4x$
 
$=-f(x)$
 
Hence the given function is an odd function.
 
It is known that $\int \limits_{-a}^a f(x)=0$ if f(x) is an odd function
 
Hence $ \int \limits_{-1}^1 x^{17}\cos ^4 xdx=0$
 
Hence proved

 

answered Mar 6, 2013 by meena.p
 
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