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leonasmart

check below for question:using integration by substitution

  • one year ago
  • one year ago

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  1. leonasmart
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    |dw:1335086576446:dw|

    • one year ago
  2. TomLikesPhysics
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    I would set u=x^3. so du=3x^2dx so x^2dx=1/3 * du. So you can rewrite it as 1/3 * (u-5)^0.5du and integrate that more easily. Of course you might wanna pull the 1/3 out and just integrate (u-5)^0.5 du and than just put it back in the end when you resubstitute.

    • one year ago
  3. leonasmart
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    do the working out for me to c plzz

    • one year ago
  4. bmp
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    Remember what I said to you. Look outside the square root, you have x^2. There must be a c such that: cx^2 = du/dx for u = x^3 - 5. That would imply that 3x^2 = cx^2 -> c = 3, so multiply by 3/3.

    • one year ago
  5. TomLikesPhysics
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    I end up with: 2/9 * (x^3-5)^(3/2) + C

    • one year ago
  6. bmp
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    \[\frac{3}{3} \int\limits_{a}^{b}x^2\sqrt{x^3 - 5}dx = \frac{1}{3} \int\limits_{u}^{v}\sqrt{u}du = \frac{1}{3} \int\limits_{u}^{v}u^{\frac{1}{2}}du\]

    • one year ago
  7. leonasmart
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    wait u is x^3-5 rite? and u is 3x^2?

    • one year ago
  8. bmp
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    Yeah, du = 3x^2. That's what I said, I belive.

    • one year ago
  9. bmp
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    du = 3x^2dx to be more precise.

    • one year ago
  10. bmp
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    @TomLikesPhysics That is correct :-)

    • one year ago
  11. leonasmart
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    • one year ago
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  12. leonasmart
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    what did i do wrong??

    • one year ago
  13. bmp
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    Remember that you have to divide by n+1, so you divide by 3/2. That's the same as multiplying by 2/3, so you have (1/3)(2/3) = 2/9. The rest is ok, well done :-)

    • one year ago
  14. Chlorophyll
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    You're absolutely correct!

    • one year ago
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