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Find the equation of a curve passing through origin if the slope of the tangent to the curve at any point (x, y) is equal to the square of the difference of the abcissa and ordinate of the point. - Mathematics

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Question

Find the equation of a curve passing through origin if the slope of the tangent to the curve at any point (x, y) is equal to the square of the difference of the abcissa and ordinate of the point.

Sum
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Solution

Here, slope of the tangent of the curve = `("d"y)/("d"x)` and the difference between the abscissa and ordinate = x – y.

∴ As per the condition, `("d"y)/("d"x) = (x - y)^2`

Put x – y = v

`1 - ("d"y)/("d"x) = "dv"/("d"x)`

∴ `("d"y)/("d"x) = 1 - "dv"/"dx"`

∴ The equation becomes `1 - "dv"/"dx" = "v"^2`

⇒ `"dv"/"dx" = 1 - "v"^2`

⇒ `"dv"/(1 - "v"^2)` = dx

Integrating both sides, we get

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

⇒ `1/2 log |(1 + "v")/(1 - "v")|` = x + c

⇒ `1/2 log|(1 + x - y)/(1 - x + y)|` = x + c  ......(1)

Since, the curve is passing through (0, 0)

Then `1/2 log|(1 + 0 - 0)/(1 - 0 + 0)|` = 0 + c

⇒ c = 0

∴ On putting c = 0 in equation (1) we get

`1/2 log |(1 + x - y)/(1 - x + y)|` = x

⇒ `log|(1 + x - y)/(1 - x + y)|` = 2x

∴ `(1 + x - y)/(1 - x + y)|` = e2x

⇒  (1 + x – y) = e2x (1 – x + y) 

Hence, the required equation is (1 + x – y) = e2x (1 – x + y).

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Chapter 9: Differential Equations - Exercise [Page 195]

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NCERT Exemplar Mathematics [English] Class 12
Chapter 9 Differential Equations
Exercise | Q 31 | Page 195

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