What Is the Correct Solution to the Differential Equation xy'^2 + yy' = 0?

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In summary, the conversation involves solving the equation xy'^2 + yy' = 0, where y' = dy/dx. The solution is C1 = y and C2 = xy. Another solution is obtained by manipulating the equation to get y' = -y/x and y = -y ln x + C2. The mistake in taking the antiderivative is pointed out and a suggestion to rearrange the equation is given.
  • #1
geft
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xy'^2 + yy' = 0 where y' = dy/dx

The answer is C1 = y and C2 = xy but I get this:

y'(xy' + y) = 0 where y' = 0 and thus y = C1

For the other solution:
xy' + y = 0
y' = -y/x
y = -y ln x + C2
C2 = y + y ln x

Full question is here: http://www.cramster.com/solution/solution/640396
 
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  • #2
geft said:
y' = -y/x
y = -y ln x + C2

You can't take the antiderivative of that expression because y is a function of x but you've treated y as a constant.

Try get the x and dx on one side, and the y and dy on the other, then integrate.
 
  • #3
Ah, I see my mistake now. Thanks!
 

Related to What Is the Correct Solution to the Differential Equation xy'^2 + yy' = 0?

1. How do I identify the degree of a polynomial?

The degree of a polynomial is determined by the highest exponent in the polynomial. For example, the degree of the polynomial 2x^3 + 5x^2 + 3x + 1 is 3.

2. What are the steps for factoring a polynomial?

The steps for factoring a polynomial include:
1. Identify any common factors between the terms
2. Use the grouping method if there are four terms
3. Use the difference of squares method if there are only two terms
4. Use the quadratic formula if the polynomial is a quadratic equation
5. Check your factored polynomial by multiplying it back out and simplifying

3. How do I solve a polynomial equation?

To solve a polynomial equation, you must first set the equation equal to zero. Then, use factoring or the quadratic formula to find the values of x that make the equation true.

4. Can I use the remainder theorem to solve a polynomial?

No, the remainder theorem is not used to solve polynomials. It is used to find the remainder when a polynomial is divided by a linear expression.

5. Is there a shortcut for solving polynomials?

Yes, there are various shortcuts for solving certain types of polynomials. Some examples include using the difference of squares method, the grouping method, or the quadratic formula. It is important to practice and familiarize yourself with these methods to efficiently solve polynomials.

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