MCQ
The solution of the equation $x\frac{{dy}}{{dx}} + 3y = x$ is
  • A
    ${x^3}y + \frac{{{x^4}}}{4} + c = 0$
  • ${x^3}y = \frac{{{x^4}}}{4} + c$
  • C
    ${x^3}y + \frac{{{x^4}}}{4} = 0$
  • D
    None of these

Answer

Correct option: B.
${x^3}y = \frac{{{x^4}}}{4} + c$
b
(b) $x\frac{{dy}}{{dx}} + 3y = x$ ==> $\frac{{dy}}{{dx}} + \frac{{3y}}{x} = 1$

It is in the form of $\frac{{dy}}{{dx}} + Py = Q$

So, $I.F.$ $ = {e^{\int_{}^{} {Pdx} }} = {e^3}^{\int_{}^{} {\frac{1}{x}dx} } = {e^{3\log x}} = {x^3}$

Hence required solution is

$y{{x}^{3}}=\int_{{}}^{{}}{{{x}^{3}}1dx\frac{{{x}^{4}}}{4}}+c=>y{{x}^{3}}=\frac{{{x}^{4}}}{4}+c$

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