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Mathematics 19 Online
OpenStudy (wade123):

HELP!

OpenStudy (wade123):

i got C @asnaseer

OpenStudy (anonymous):

@AMYCARTER

OpenStudy (wade123):

@SithsAndGiggles PLEASE HELP

OpenStudy (wade123):

i just need someone to check my answer please

OpenStudy (anonymous):

Have you tried solving any of these ODEs? They are all separable, so not too difficult.

OpenStudy (anonymous):

Before you try that, though, I'm sure there's an easier (but somewhat tedious) way to approach this. Pick some points from the graph, like the \((1,1)\) and \((-1,-1)\), for example, and plug them into the DE. This way you can eliminate which ODEs are NOT satisfied. For example, take \((-1,-1)\). You get \[\begin{matrix}\frac{dy}{dx}_A=\frac{-1}{(-1)^2}=-1&&\frac{dy}{dx}_B=\frac{-1}{-1}=1\\\\ \frac{dy}{dx}_C=\frac{(-1)^2}{-1}=-1&&\frac{dy}{dx}_D=\frac{(-1)^2}{(-1)^2}=1 \end{matrix}\] According to the slope field, at \((-1,-1)\), the slope appears to be negative, so you can eliminate B and D.

OpenStudy (wade123):

thats such a more simple way to do it...i took up like a whole page

OpenStudy (wade123):

but i think we both got the same answer whih was C

OpenStudy (anonymous):

Yes, that's right. If you try the point \((-1,1)\) or \((1,-1)\), you'll eliminate A.

OpenStudy (wade123):

thanks so much(:

OpenStudy (wade123):

it would be parabolas right?

OpenStudy (wade123):

@SithsAndGiggles

OpenStudy (anonymous):

Not parabolas, no. You can tell by solving - there are a few ways, but treating this as a separable is easiest. \[\begin{align*}x\,dx+y\,dy&=0\\ y\,dy&=-x\,dx\\ \int y\,dy&=-\int x\,dx\\ \frac{1}{2}y^2&=-\frac{1}{2}x^2+C\\ y^2+x^2&=C^* \end{align*}\] Which conic is this?

OpenStudy (wade123):

hyperbola @SithsAndGiggles

OpenStudy (anonymous):

No, not hyperbola

OpenStudy (wade123):

oh wait circle

OpenStudy (wade123):

right? @SithsAndGiggles

OpenStudy (anonymous):

Yes, a circle. Remember, \(x^2+y^2=r^2\) is a circle with radius \(r\).

OpenStudy (wade123):

thanks for the help(:

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