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Ira Lisetskai [31]
3 years ago
7

Find all the solutions for the equation:

Mathematics
1 answer:
Contact [7]3 years ago
7 0

2y^2\,\mathrm dx-(x+y)^2\,\mathrm dy=0

Divide both sides by x^2\,\mathrm dx to get

2\left(\dfrac yx\right)^2-\left(1+\dfrac yx\right)^2\dfrac{\mathrm dy}{\mathrm dx}=0

\dfrac{\mathrm dy}{\mathrm dx}=\dfrac{2\left(\frac yx\right)^2}{\left(1+\frac yx\right)^2}

Substitute v(x)=\dfrac{y(x)}x, so that \dfrac{\mathrm dv(x)}{\mathrm dx}=\dfrac{x\frac{\mathrm dy(x)}{\mathrm dx}-y(x)}{x^2}. Then

x\dfrac{\mathrm dv}{\mathrm dx}+v=\dfrac{2v^2}{(1+v)^2}

x\dfrac{\mathrm dv}{\mathrm dx}=\dfrac{2v^2-v(1+v)^2}{(1+v)^2}

x\dfrac{\mathrm dv}{\mathrm dx}=-\dfrac{v(1+v^2)}{(1+v)^2}

The remaining ODE is separable. Separating the variables gives

\dfrac{(1+v)^2}{v(1+v^2)}\,\mathrm dv=-\dfrac{\mathrm dx}x

Integrate both sides. On the left, split up the integrand into partial fractions.

\dfrac{(1+v)^2}{v(1+v^2)}=\dfrac{v^2+2v+1}{v(v^2+1)}=\dfrac av+\dfrac{bv+c}{v^2+1}

\implies v^2+2v+1=a(v^2+1)+(bv+c)v

\implies v^2+2v+1=(a+b)v^2+cv+a

\implies a=1,b=0,c=2

Then

\displaystyle\int\frac{(1+v)^2}{v(1+v^2)}\,\mathrm dv=\int\left(\frac1v+\frac2{v^2+1}\right)\,\mathrm dv=\ln|v|+2\tan^{-1}v

On the right, we have

\displaystyle-\int\frac{\mathrm dx}x=-\ln|x|+C

Solving for v(x) explicitly is unlikely to succeed, so we leave the solution in implicit form,

\ln|v(x)|+2\tan^{-1}v(x)=-\ln|x|+C

and finally solve in terms of y(x) by replacing v(x)=\dfrac{y(x)}x:

\ln\left|\frac{y(x)}x\right|+2\tan^{-1}\dfrac{y(x)}x=-\ln|x|+C

\ln|y(x)|-\ln|x|+2\tan^{-1}\dfrac{y(x)}x=-\ln|x|+C

\boxed{\ln|y(x)|+2\tan^{-1}\dfrac{y(x)}x=C}

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The question is incomplete. Here is the complete question:

A machine covers 5/8 square foot in 1/4 hour. what is the unit rate?

Answer:

2.5 square feet per hour

Step-by-step explanation:

Given:

Area covered by a machine = frac{5}{8}\ ft^2

Time taken to cover the given area = \frac{1}{4}\ h

Now, unit rate of the first quantity with respect to second quantity is the magnitude of the first quantity being when the second quantity is one unit.

Here, the first quantity is the area covered and the second quantity is the time taken.

So, unit rate is the area covered by the machine in 1 hour.

In order to find that, we use the unitary method and divide the area by the total time taken. Therefore,

Unit\ rate=\frac{Total\ area\ covered}{Total\ time\ taken}\\\\Unit\ rate=(\frac{5}{8}\ ft^2)\div (\frac{1}{4}\ h)\\\\Unit\ rate=\frac{5}{8}\times \frac{4}{1}\ ft^2/h\\\\Unit\ rate=\frac{20}{8}=2.5\ ft^2/h

Thus, the unit rate is 2.5 square feet per hour.

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Step-by-step explanation:

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