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lilMissMindset

  • 3 years ago

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

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  1. him1618
    • 3 years ago
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    You can try substituting y = asinx + bcosx

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

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

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

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

  6. him1618
    • 3 years ago
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    that is for a special case i think

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

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

  9. lilMissMindset
    • 3 years ago
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    that is for the homo part

  10. him1618
    • 3 years ago
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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

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

  12. him1618
    • 3 years ago
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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

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

  14. him1618
    • 3 years ago
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    Your welcome

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