Q42 / 90 · JEE Main 2019 (09 Apr Shift 1) · Mathematics

The solution of the differential equation xdydx+2y=x2, (x≠0) with y1=1, is

  • A
    y=x35+15x2
  • B
    y=34x2+14x2
  • Correct answer
    C
    y=x24+34x2
  • D
    y=45x3+15x2

Solution

Given, differential equation is dydx+2xy=x

This is a linear differential equation of type dydx+Py=Q, where P & Q are the functions of x or constants.

Thus, P=2x & Q=x

The integrating factor I.F.=e∫Pdx

=e∫2x dx=e2lnx

=elnx2=x2.

The solution of the linear differential equation is y×I.F.=∫Q×I.F.dx+C 

So, the solution of the given differential equation is

yx2=∫x·x2dx+C

⇒x2y=∫x3dx+C

Using ∫xndx=xn+1n+1, we get

⇒x2y=x44+C

Since y1=1

⇒1·1=14+C

⇒C=34

⇒x2y=x44+34

 ⇒y=x24+34x2.

Hence, the correct answer is option: 'C'.

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