Back Substitution - When a u-sub doesn't match cleanly!

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  • เผยแพร่เมื่อ 10 ม.ค. 2025

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  • @jackcordonnier6421
    @jackcordonnier6421 7 ปีที่แล้ว +42

    I believe there was an error made in the second problem since you wrote down -4 at one part when you said plus 4 so the final answer is as far as i can tell not correct.

    • @DrTrefor
      @DrTrefor  4 ปีที่แล้ว +11

      Agreed, good catch!

    • @sachinmr3096
      @sachinmr3096 4 ปีที่แล้ว +1

      Yep there is error in last part of second question... 😊

    • @Lukav1
      @Lukav1 2 ปีที่แล้ว +1

      Yeah I was just thinking why does 4 change to -4, tnx for pointing it out

    • @sizzle9324
      @sizzle9324 ปีที่แล้ว +2

      @@Lukav1 dudes having a conversation over the past half decade

    • @tncreations1267
      @tncreations1267 ปีที่แล้ว

      @@sizzle9324 Yeah 😂

  • @CalebRyals
    @CalebRyals 2 ปีที่แล้ว +3

    You could make #2 a lot simpler by separating the parts of your numerator prior to the back sub for the x^2, making it a lot simpler, and less confusing to come away with 1/2u^2-4u+8lnu.

  • @sajdak1279
    @sajdak1279 27 วันที่ผ่านมา

    WHAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAATTTTTTTTTTTTTTTTTTTTTTTTTTTTT MY JAW DROPPED THATS SO COOL

  • @magokulo1341
    @magokulo1341 13 วันที่ผ่านมา

    Found the correct answer for the original problem I think:
    S( (x^2 +4) / (x+2) dx ) = (x^2)/2 - 2x - 6 + 8*Ln(x+2) + C
    let u = x+2 --> x = u-2 --> du=dx,
    S( (x^2 + 4)/(x+2) dx) = S( ( (u-2)^2 +4 )/u du ) = S( (u^2 -4u +4 +4)/u du )
    =S( (u^2 -4u +8)*u^-1 du ) = S( u - 4 + 8 (1/u) du )
    S( u^2 du ) - S (4 du ) + 8*S( 1/u du) = (u^2)/2 - 4u +8(Ln(u)) + C
    = ( (x+2)^2)/2 - 4(x+2) + 8*Ln(x+2) + C = (x^2 +4x +4)/2 - 4x - 8 + 8*ln(x+2) + C
    = (x^2)/2 +2x +2 -4x -8 +8*ln(x+2) + C = (x^2)/2 -2x -6 + 8*ln(x+2) + C
    Kinda hard to read on a comments sections with no math symbols but hopefully one can read it.

  • @sizzle9324
    @sizzle9324 ปีที่แล้ว +1

    sigma