Eliminate the arbitrary constant in the equation: X^3 -3x^2y=C

1 answer

To eliminate the arbitrary constant \( C \) from the equation \( x^3 - 3x^2y = C \), we can rearrange the equation in terms of \( y \).

Starting with the equation:

\[ x^3 - 3x^2y = C \]

we can express \( y \) as:

\[ 3x^2y = x^3 - C \]

Now, divide both sides by \( 3x^2 \) to solve for \( y \):

\[ y = \frac{x^3 - C}{3x^2} \]

To eliminate the constant \( C \), we take partial derivatives of \( y \) with respect to \( x \) and \( C \).

  1. Differentiate \( y \) with respect to \( x \) while treating \( C \) as a constant:

\[ \frac{\partial y}{\partial x} = \frac{3x^2(1) - (x^3 - C)(2x)}{(3x^2)^2} \]

  1. Differentiate \( y \) with respect to \( C \):

\[ \frac{\partial y}{\partial C} = -\frac{1}{3x^2} \]

Next, we can use the condition that keeps \( C \) constant and these derivatives equal. Setting the determinant (Jacobian) of the transformation formed by the variables to zero could be a way to eliminate \( C \).

In this case, we can eliminate \( C \) by considering the dependency of \( y \) on \( C \) through the derivatives. Hence, using the derivatives, we can set up a relation:

\[ 3x^2 \frac{\partial y}{\partial x} + \frac{\partial y}{\partial C} = 0 \]

This will provide a differential equation independent of \( C \).

However, it is more illustrative in this case simply to recognize that the original equation itself represents a relationship between \( x \) and \( y \) that does not need C explicitly, showing its dependence.

To encapsulate everything, the resultant form shows the implicit relationship between \( x \) and \( y \):

\[ x^3 - 3x^2y = 0 \]

This can also be expressed as:

\[ y = \frac{x^3}{3x^2} \]

or simply recognizing that:

\[ y = \frac{x}{3} \quad (x \neq 0) \]

Thus, the arbitrary constant \( C \) has been eliminated in terms of the direct relationship between \( x \) and \( y \).