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bii17 Group Title

integrate (x)(cos^3 x) dx

  • one year ago
  • one year ago

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  1. sirm3d Group Title
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    do you know the reduction formula for \[\int \cos^n x \,\mathrm dx\]

    • one year ago
  2. bii17 Group Title
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    reduction?? nope...

    • one year ago
  3. matricked Group Title
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    first simplify cos^3 x in terms of cosine of 3x and x and then integrate by parts

    • one year ago
  4. matricked Group Title
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    i don't think here u should use reduction formula

    • one year ago
  5. bii17 Group Title
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    its \[\cos ^3 x\] .. where did u get 3x and x @matricked

    • one year ago
  6. matricked Group Title
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    use cos3x =4 cos^3 (x) - 3cos x

    • one year ago
  7. sirm3d Group Title
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    why not? it solves the problem too, but the solution may not be attractive to @bii17

    • one year ago
  8. matricked Group Title
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    i mean use cos^3 (x) =1/4 *(cos3x +3cosx)

    • one year ago
  9. bii17 Group Title
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    oh okay.. then what will happen next ? @matricked

    • one year ago
  10. matricked Group Title
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    and then use by parts

    • one year ago
  11. bii17 Group Title
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    \[1/4 [x(\cos 3x + 3\cos x)]dx\] is this correct? @matricked

    • one year ago
  12. matricked Group Title
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    yup

    • one year ago
  13. bii17 Group Title
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    so there will be u and du den dv and v... i used Dv as cos 3x dx the V will be 1/3 sin 3x ???

    • one year ago
  14. matricked Group Title
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    for both integration of 1/4 *xcos3x take x as the first function

    • one year ago
  15. bii17 Group Title
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    i get it.. thanks a lot :) @matricked

    • one year ago
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