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The differential equation `(dy)/(dx)=(x+y-1)/(x+y+1)` reduces to variable separable form by making the substitutionA. `x+y=v`B. `x-y=v`C. `y=vx`D. `x=vy`

Answer» Correct Answer - A
Let `x+y=v`. Then, `1+(dy)/(dx)=(dv)/(dx)`
Substituting these values in the given differential equaiton, we get
`(dv)/(dx)-1=(v-1)/(v+1)rArr (dv)/(dx)=(2v)/(v+1)rArr(v+1)/(2v)dv=dx`
Clearly, it is in variable separable form.


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