मराठी

Solcve: ddxdydx=y(logy–logx+1)

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प्रश्न

Solcve: `x ("d"y)/("d"x) = y(log y – log x + 1)`

बेरीज
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उत्तर

Given that: `x ("d"y)/("d"x) = y(log y – log x + 1)`

⇒ `x ("d"y)/("d"x) = y[log(y/x) + 1]`

⇒ `("d"y)/("d"x) = y/x[log(y/x) + 1]`

Since, it is a homogeneous differential equation.

∴ Put y = vx

⇒ `("d"y)/("d"x) = "v" + x * "dv"/"dx"`

∴ `"v" + x * "dv"/"dx" = "vx"/x[log("vx"/x) + 1]`

⇒ `"v" + x * "dv"/"dx" = "v"[log "v" + 1]`

⇒ `x * "dv"/"dx" = "v"[log "v" + 1] - "v"`

⇒ `x * "dv"/"dx"` = v  ....[log v + 1 – 1]

⇒ `x * "dv"/"dx" = "v" * log "v"`

⇒ `"dv"/("v"log"v") = "dx"/x`

Integrating both sides, we get

`int "dv"/("v"log"v") = int "dx"/x`

Put log v = t on L.H.S.

`1/"v" "dv"` = dt

∴ `int "dt"/"t" = int "dx"/x`

`log|"t"| = log|x| + log"c"`

⇒ `log|log "v"| = log x"c"`

⇒ log v = xc

⇒ `log(y/x)` = xc

Hence, the required solution is `log(y/x)` = xc.

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पाठ 9: Differential Equations - Exercise [पृष्ठ १९५]

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एनसीईआरटी एक्झांप्लर Mathematics Exemplar [English] Class 12
पाठ 9 Differential Equations
Exercise | Q 33 | पृष्ठ १९५

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