The function u(x, y) = c which satisfies the differential equation

x(dx - dy) + y(dy - dx) = 0, is

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  1. \(\rm x^2+y^2=xy+c\)
  2. \(\rm x^2+y^2 =4xy+c\)
  3. \(\rm x^2-y^2=xy+c \)
  4. \(\rm x^2 -y^2=2xy+c\)

Answer (Detailed Solution Below)

Option 2 : \(\rm x^2+y^2 =4xy+c\)
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Detailed Solution

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Concept:

In ∫x dy, x will be considered as constant

In ∫x dy, x will be considered as constant

Formula Used:

∫xndx = xn+1/(n+1)

Calculation:

Here, x(dx - dy) + y(dy - dx) = 0

⇒ xdx - x dy + ydy - ydx = 0

Taking integration, we get 

∫ xdx - ∫ x dy + ∫ ydy - ∫ ydx = 0

By using the above formula 

⇒ \(\rm \frac{x^2}{2}-xy+\frac{y^2}{2}-xy+c=0\\ \)

⇒ \(\rm x^2+y^2-4xy+c=0\)

\(\Rightarrow \rm x^2+y^2 =4xy+c\)

Hence, option (2) is correct. 

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