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Solve dydxx2dydx-xy=1+cos(yx), x ≠ 0 and x = 1, y = π2

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Question

Solve `x^2 "dy"/"dx" - xy = 1 + cos(y/x)`, x ≠ 0 and x = 1, y = `pi/2`

Sum
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Solution

Given equation can be written as

`x^2 "dy"/"dx" - xy = 2cos^2 (y/2x)`, x ≠ 0.

⇒ `(x^2 "dy"/"dx" - xy)/(2cos^2 (y/(2x))` = 1

⇒ `sec^2 (y/(2x))/2 [x^2 "dy"/"dx" - xy]` = 1

Dividing both sides by x3, we get

`sec^2(y/(2x))/2 [(x "dy"/"dx" - y)/x^2] = 1/x^3`

⇒ `"d"/"dx"[tan(y/(2x))] = 1/x^3`

Integrating both sides, we get

`tan(y/(2x)) = (-1)/(2x^2) + "k"`

Substituting x = 1, y = `pi/2`, we get

k = `3/2`

Therefore, `tan(y/(2x)) = -1/(2x^2) + 3/2` is the required solution.

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Chapter 9: Differential Equations - Solved Examples [Page 185]

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NCERT Exemplar Mathematics Exemplar [English] Class 12
Chapter 9 Differential Equations
Solved Examples | Q 10 | Page 185

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