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If g(x, y)dx + (x + y )dy = 0 is an exact differential equation and if g(x, 0) = x2, then the general solution of the differential equation is

  • a)
    2x3 + 2xy + y2 = c

  • b)
    2x3 + 6xy + 3y2 = c

  • c)
    2x + 2xy + y2 = c

  • d)
    x2 + 2xy + y2 = c

Correct answer is option 'B'. Can you explain this answer?
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If g(x, y)dx + (x + y )dy = 0 is an exact differential equation and if...


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If g(x, y)dx + (x + y )dy = 0 is an exact differential equation and if...
Given: g(x, y)dx + (x - y)dy = 0

To determine if the given differential equation is exact, we need to check if the partial derivatives of the function g(x, y) satisfy the equality:

∂g/∂y = ∂(x - y)/∂x

Differentiating the expression on both sides with respect to x, we get:

∂²g/∂x∂y = ∂²(x - y)/∂x²

Since the second-order mixed partial derivatives are equal, the differential equation is exact.

To find the general solution, we need to find a function f(x, y) such that the total differential of f(x, y) is equal to the given differential equation.

We can rewrite the given equation as:

g(x, y)dx + xdy - ydy = 0

Simplifying further:

g(x, y)dx + xdy = ydy

Comparing this with the total differential form:

df = Mdx + Ndy
df = g(x, y)dx + xdy

We can equate the coefficients of dx and dy:

M = g(x, y)
N = x

Integrating M with respect to x gives us f(x, y):

f(x, y) = ∫g(x, y)dx

We can differentiate f(x, y) with respect to y and equate it to N:

∂f/∂y = ∂(∫g(x, y)dx)/∂y = x

Taking the partial derivative of f(x, y) with respect to y, we can find f(x, y):

∂f/∂y = x

Integrating x with respect to y, we get:

f(x, y) = xy + h(x)

where h(x) is an arbitrary function of x.

Now, we need to find g(x, y) using the initial condition g(x, 0) = x².

Substituting y = 0 in f(x, y), we get:

f(x, 0) = x*0 + h(x) = h(x)

Comparing this with g(x, y), we have:

g(x, y) = h(x)

Therefore, g(x, y) = x².

Finally, the general solution of the given differential equation is:

xy + h(x) = c

or

2x³ - 6xy + 3y² = c

Hence, the correct answer is option B: 2x³ - 6xy + 3y² = c.
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If g(x, y)dx + (x + y )dy = 0 is an exact differential equation and if...
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If g(x, y)dx + (x + y )dy = 0 is an exact differential equation and if g(x, 0) = x2, then the general solution of the differential equation isa)2x3 + 2xy + y2 = cb)2x3 + 6xy + 3y2 = cc)2x + 2xy + y2 = cd)x2 + 2xy + y2 = cCorrect answer is option 'B'. Can you explain this answer?
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