The solution of the differential equation (x2 + y2 )dx - 5xy dy = 0, y(1) = 0, is :
- |x2 - 4y2 |5 = x2
- |x2 - 2y2 |6 = x
- |x2 - 2y2 |5 = x2
- |x2 - 4y2 |6 = x
Answer
(1) |x2 - 4y2 |5 = x2
Solution
dydx = x2 + y25xy is homogeneous, so put y = vx:
v + x dvdx = 1 + v25v x dvdx = 1 - 4v25v
5v1 - 4v2 dv = dxx
- 58 |1 - 4v2 | = |x| + c
|1 - 4v2 |5 x8 = C |x2 - 4y2 |5 = Cx2 (using v = yx)
Since y(1) = 0, C = 1, hence |x2 - 4y2 |5 = x2
Answer: (1)