# Math Help - Confusing Differential Equation

1. ## Confusing Differential Equation

I'm trying to solve y'=-sqrt(|xy|).

Not too sure on how to handle the absolute value signs.

I've tried solving for +/-x and +/-y, but i couldn't find the constants because it involved negative square roots.

Any ideas?

Thanks

2. Originally Posted by benw
I'm trying to solve y'=-sqrt(|xy|).

Not too sure on how to handle the absolute value signs.

I've tried solving for +/-x and +/-y, but i couldn't find the constants because it involved negative square roots.

Any ideas?

Thanks
Split it up into two equations, and solve them separately.

$\frac{dy}{dx} = - \sqrt{xy}$

$\frac{dy}{dx} = - \sqrt{-xy}$

3. I tried doing that. For example y'=-sqrt(-xy)

dx/sqrt(-x)=-sqrt(y)dy

2x/sqrt(-x)+c=2.sqrt(y).y/3

now say it is given that x(0)=1, c=sqrt(-1)/2(-1). I wouldn't be able to work out the constant here?

Or does it simply mean that i do not need to solve for

dx/sqrt(-x)=-sqrt(y)dy

and only need to solve for

dx/sqrt(x)=-sqrt(-y)dy?

Thanks