CBSE Class 12 Math 2013 Solved Paper

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Question : 26 of 29
 
Marks: +1, -0
Show that the differential equation 2yex∕y dx + (y - 2x ex∕y) dy is homogeneous. Find the particular solution of this differential equation, given that x = 0 when y = 1.= 0
Solution:
2yex∕y dx + (y - 2x ex∕y) dy = 0
dxdy = 2xexy−y2yexy ... (1)
Let f (x , y) = 2xexy−y2yexy
Then, (λx , λy) = λ(2xexy−y)λ(2yexy) = λ0 [F (x,y)]
Thus, F(x, y) is a homogeneous function of degree zero. Therefore, the given differential equation is a homogeneous differential equation.
Let x = vy
Differentiating w.r.t. y, we get
dxdy = v + y dvdy
Substituting the value of x and dxdy in equation (1), we get
v + y dvdy = 2vyev−y2yev = 2vev−12ev
or y dvdy = 2vev−12ev - v
or y dvdy = - 12ev
or 2ev dv = - dyy
or ∫ 2ev . dv = - ∫ dyy
or 2ev = - log |y| + C
Substituting the value of v, we get
2eπy + log |y| = C ... (2)
Substituting x = 0 and y = 1 in equation (2), we get
2e0 + log |1| = C ⇒ C = 2
Substituting the value of C in equation (2), we get
2exy + log |y| = 2, which is the particular solution of the given differential equation.
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