# Solve the following differential equation. (x2 − y2 ) dx + 2xy dy = 0 - Mathematics and Statistics

Sum

Solve the following differential equation.

(x2 − y2 ) dx + 2xy dy = 0

#### Solution

(x2 − y2 ) dx + 2xy dy = 0

∴ 2xy dy = (y2 - x2) dx

∴ dy/dx = (y^2 - x^2)/(2xy) ......(i)

Put y = tx  ...(ii)

Differentiating w.r.t. x, we get

dy/dx = t +x dt/dx  ...(iii)

Substituting (ii) and (iii) in (i), we get

t + x dt/dx = (t^2 x^2-x^2)/(2tx^2)

∴ x dt/dx = (t^2 - 1)/(2t )- t = (-(1+t^2))/(2t)

∴ 2t/(1+t^2) dt = - dx/x

Integrating on both sides, we get

int 2t/(1+t^2) dt = - int dx/x

∴ log |1 + t2| = -log |x| + log |c|

∴log | 1+y^2/x^2| = log |c/x|

∴ (x^2 + y^2)/x^2 = c/x

∴  x2 + y2 = cx

Concept: Differential Equations
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#### APPEARS IN

Balbharati Mathematics and Statistics 1 (Commerce) 12th Standard HSC Maharashtra State Board
Chapter 8 Differential Equation and Applications
Exercise 8.4 | Q 1.5 | Page 167