Solve the  differential equation: from Mathematics Differenti

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 Multiple Choice QuestionsShort Answer Type

191.

Solve the  differential equation:
straight x squared dy over dx space equals straight y left parenthesis straight x plus straight y right parenthesis.

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 Multiple Choice QuestionsLong Answer Type

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192.

Solve the  differential equation:
left parenthesis straight y plus straight x right parenthesis space dy over dx space equals space straight y minus straight x.


The given differential equation is
                   left parenthesis straight y plus straight x right parenthesis space dy over dx space equals space straight y minus straight x
therefore space space space space space space space dy over dx space equals space fraction numerator straight y minus straight x over denominator straight y plus straight x end fraction                             ...(1)
Put y = v x  so that dy over dx space equals space straight v plus straight x dv over dx
therefore       from (1),    straight v plus straight x dv over dx space equals space fraction numerator vx minus straight x over denominator vx plus straight x end fraction
therefore space space space space straight v plus straight x dv over dx space equals space fraction numerator straight v minus 1 over denominator straight v plus 1 end fraction space space space space space space space space space space space space space or space space space space space space space straight x dv over dx equals fraction numerator straight v minus 1 over denominator straight v plus 1 end fraction minus straight v
or            straight x dv over dx space equals fraction numerator straight v minus 1 minus straight v squared minus straight v over denominator straight v plus 1 end fraction space space space space or space space space space straight x dv over dx space equals space minus fraction numerator 1 plus straight v squared over denominator 1 plus straight v end fraction
Separating the variables, we get,
                   fraction numerator 1 plus straight v over denominator 1 plus straight v squared end fraction dv space equals space minus 1 over straight x dx
Integrating,  integral fraction numerator 1 plus straight v over denominator 1 plus straight v squared end fraction dv equals space minus integral 1 over straight x dx
therefore space space space space integral fraction numerator 1 over denominator 1 plus straight v squared end fraction dv plus 1 half integral fraction numerator 2 straight v over denominator 1 plus straight v squared end fraction dv space equals space minus integral 1 over straight x dx
therefore space space space space tan to the power of negative 1 end exponent straight v plus 1 half log space left parenthesis 1 plus straight v squared right parenthesis space equals space minus log space open vertical bar straight x close vertical bar space plus space straight c subscript 1
therefore space space space space space tan to the power of negative 1 end exponent open parentheses straight y over straight x close parentheses plus 1 half log open parentheses 1 plus straight y squared over straight x squared close parentheses space equals space minus log space open vertical bar straight x close vertical bar plus straight c subscript 1
therefore space space space space space 2 space tan to the power of negative 1 end exponent open parentheses straight y over straight x close parentheses plus log space open parentheses fraction numerator straight x squared plus straight y squared over denominator straight x squared end fraction close parentheses space equals space minus log open vertical bar straight x close vertical bar squared plus 2 straight c subscript 1
therefore space space space space space 2 space tan to the power of negative 1 end exponent open parentheses straight y over straight x close parentheses plus log space open parentheses fraction numerator straight x squared plus straight y squared over denominator straight x squared end fraction close parentheses space equals space minus log space straight x squared plus straight c
therefore space space space 2 space tan to the power of negative 1 end exponent open parentheses straight y over straight x close parentheses plus log space open parentheses fraction numerator straight x squared plus straight y squared over denominator straight x squared end fraction close parentheses plus log space straight x squared space equals space straight c
therefore space space space 2 space tan to the power of negative 1 end exponent open parentheses straight y over straight x close parentheses plus log space open parentheses fraction numerator straight x squared plus straight y squared over denominator straight x squared end fraction cross times space straight x squared close parentheses space equals space straight c
therefore space space space 2 space tan to the power of negative 1 end exponent open parentheses straight y over straight x close parentheses plus log space open parentheses straight x squared plus straight y squared close parentheses space equals space straight c
which is required solution.
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193.

Solve the following differential equation:
(y2 – x2) dy = 3 x y dx

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194. Show that the following differential equation is homogeneous and find a primitive of it. Derive the solution wherever possible:
(x - y) y' = x + 2 y 
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195. Show that the following differential equation is homogeneous and find a primitive of it. Derive the solution wherever possible:
(x2 + y2) y' = 8 x2 - 3 x y + 2 y2
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196. Show that the following differential equation is homogeneous and find a primitive of it. Derive the solution wherever possible:
(3 x y + y2) dx = (x2 + x y) dy
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197. Show that the following differential equation is homogeneous and find a primitive of it. Derive the solution wherever possible:
2 x y dx + (x2 + 2 y2) dy = 0
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198. Show that the following differential equation is homogeneous and find a primitive of it. Derive the solution wherever possible:
left parenthesis 2 straight x squared straight y plus straight y cubed right parenthesis space dx plus space left parenthesis xy squared minus 3 straight x cubed right parenthesis space dy space equals space 0
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 Multiple Choice QuestionsShort Answer Type

199. Show that the following differential equation is homogeneous and find a primitive of it. Derive the solution wherever possible:
straight x space straight y apostrophe space minus space straight y space plus space straight x space sin space space open parentheses straight y over straight x close parentheses space equals 0
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 Multiple Choice QuestionsLong Answer Type

200. Show that the following differential equation is homogeneous and find a primitive of it. Derive the solution wherever possible:
left parenthesis straight x plus 2 straight y right parenthesis space dx space minus space left parenthesis 2 straight x minus straight y right parenthesis space dy space equals space 0
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