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lilMissMindset

this one is tricky. help please! y''-4y'+3y=2cosx+4sinx i'm having trouble getting the Yp!

  • one year ago
  • one year ago

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  1. him1618
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    You can try substituting y = asinx + bcosx

    • one year ago
  2. ChmE
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    why would that help. I'm in diff eq as well and I wasn't thinking about that.

    • one year ago
  3. him1618
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    its called th method of undetermined coefficients

    • one year ago
  4. him1618
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    put it on the left side....compare with coeffs on the right fr etermining a a and b

    • one year ago
  5. lilMissMindset
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    isn't it y=a cos x + b sinx + cx cos x + dx sin x

    • one year ago
  6. him1618
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    that is for a special case i think

    • one year ago
  7. lilMissMindset
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    what are the roots anyway? +i, -i aren't they like, twice? then it will be case 4?

    • one year ago
  8. ChmE
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    r^2 - 4r +3 = 0 (r - 3)(r-1) r= 3, 1

    • one year ago
  9. lilMissMindset
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    that is for the homo part

    • one year ago
  10. him1618
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    im telling you take y=asinx + bcosx substitute y'' and y' and y in the above eqn and compare LHS and RHS ull get 2 eqns in a and b determine a and b and you have your soln

    • one year ago
  11. lilMissMindset
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    i did that, i always get 0 for B. it's not supposed to be the answer.

    • one year ago
  12. him1618
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    im getting the answer as b=1, a=0 which means y=cos x y=cos x satisfies the above eqns

    • one year ago
  13. lilMissMindset
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    oh sorry. i looked at the wrong answer on my book. i am sorry. Our answer is right. Thank you!

    • one year ago
  14. him1618
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    Your welcome

    • one year ago
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