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Solve the following differential equation: y2 dx + (xy + x2)dy = 0

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प्रश्न

Solve the following differential equation:

y2 dx + (xy + x2)dy = 0

योग
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उत्तर

y2 dx + (xy + x2)dy = 0

∴ (xy + x2)dy = - y2 dx

∴ `"dy"/"dx" = (- "y"^2)/("xy + x"^2)`

Put y = vx

∴ `"dy"/"dx" = "v + x""dv"/"dx"`

Substituting these values in (1), we get

`"v + x""dv"/"dx" = (- "v"^2"x"^2)/("x" * "vx + x"^2) = (- "v"^2)/("v + 1")`

∴ `"x" "dv"/"dx" = (- "v"^2)/("v + 1") - "v" = (- "v"^2 - "v"^2 - "v")/("v + 1")` 

∴ `"x" "dv"/"dx" = (- 2"v"^2 - "v")/("v + 1") = -(("2v"^2 + "v")/("v + 1"))`

∴ `("v + 1")/("2v"^2 + "v")"dv" = - 1/"x" "dx"`

Integrating both sides, we get

`int ("v + 1")/("2v"^2 + "v")"dv" = - int 1/"x" "dx"`

∴`int ("v + 1")/("v"("2v" + 1))"dv" = - int 1/"x" "dx"`

∴ `int(("2v" + 1) - "v")/("v"("2v" + 1))"dv" = - int 1/"x" "dx"`

∴ `int(1/"v" - 1/("2v + 1"))"dv" = - int 1/"x" "dx"`

∴ `int 1/"v" "dv" - int1/("2v + 1")"dv" = - int 1/"x" "dx"`

∴ `log |"v"| - 1/2 log |2"v" + 1| = - log |"x"| + log "c"`

∴ `2 log |"v"| - log |2"v" + 1| = - 2 log |"x"| + 2 log "c"`

∴ `log |"v"^2| - log |"2v" + 1| = - log |"x"^2| + log "c"^2`

∴ `log |"v"^2/("2v" + 1)| = log |"c"^2/"x"^2|`

∴ `"v"^2/("2v" + 1) = "c"^2/"x"^2`

∴ `("y"^2/"x"^2)/(2 ("y"/"x") + 1) = "c"^2/"x"^2`

∴ `"y"^2/("x"("2y + x")) = "c"^2/"x"^2`

∴ xy2 = c2(x + 2y)

This is the general solution.

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  क्या इस प्रश्न या उत्तर में कोई त्रुटि है?
अध्याय 6: Differential Equations - Exercise 6.4 [पृष्ठ २०३]

APPEARS IN

बालभारती Mathematics and Statistics 2 (Arts and Science) [English] Standard 12 Maharashtra State Board
अध्याय 6 Differential Equations
Exercise 6.4 | Q 4 | पृष्ठ २०३

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