Q.

Let  y=y(x) be the solution curve of the differential equation dydx=yx(1+xy2(1+logex)),x>0,y(1)=3 . Then  y2(x)9 is equal to: 

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a

x273x3(2+logex2)

b

x252x3(2+logex3)

c

x22x3(2+logex3)3

d

x23x3(1+logex2)2

answer is A.

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Detailed Solution

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dydxyx=y3(1+lnx)1y3dydx1xy2=(1+lnx)Taking1y2=t2y3dydx=dtdx12dtdxtx=(1+lnx)dtdx+2tx=2(1+lnx)I.F.=e2xdx=x2tx2=2(1+lnx)x2dxtx2=2[(1+lnx)x33x23dx]+cx2y2=2[x33(1+lnx)x39]+c........(i)y(1)=319=2(1319)+cc=59
x2y2=2x33(1+lnx)x39+59y29=x252x32+lnx3

Explanation:

To solve the given differential equation dydx=yx(1+xy2(1+lnx)) with the initial condition y(1)=3, we will follow these steps:

Step 1: Rearranging the Differential Equation
We start with the equation:
dydx=yx(1+xy2(1+lnx))
We can rewrite this as:
dydx=yx+xy3(1+lnx)x
This simplifies to:
dydx=yx+y3(1+lnx)

Step 2: Separating Variables
We can separate the variables:
dyy3=(1+lnx)dx−1xdy
Rearranging gives us:
dyy3=(1+lnx−1x)dx

Step 3: Integrating Both Sides
Now we integrate both sides:
∫dyy3=∫(1+lnx−1x)dx
The left side integrates to:
−12y2
The right side can be integrated term by term:
∫1dx+∫lnxdx−∫1xdx=x+xlnx−x+C
Thus, we have:
−12y2=xlnx+C

Step 4: Applying the Initial Condition
Using the initial condition y(1)=3:
−12(32)=1⋅ln(1)+C
This simplifies to:
−118=0+C⟹C=−118

Step 5: Substituting Back
Substituting C back into our equation gives:
−12y2=xlnx−118
Multiplying through by -2:
1y2=−2xlnx+19

Step 6: Finding y29
Rearranging gives:
y2=91−18xlnx
Thus, we find:
y29=11−18xlnx

Final Answer
The value of y2(x)9 is:
y2(x)9=11−18xlnx

 

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