Question 89 of 96intermediate🔧 ApplyLong Answer4 marks

Solve the differential equation yexydx=(xexy+y2)dyy e^{\frac{x}{y}} dx = \left(x e^{\frac{x}{y}} + y^2\right) dy (y≠0)(y \neq 0).

Correct Answer

The general solution of the given differential equation is:

exy=y+Ce^{\frac{x}{y}} = y + C
Exercise: Miscellaneous Exercise on Chapter 9 | Q: 8 | (Page 34)
For More Understanding

Explanation

This is a homogeneous differential equation. The substitution method using v=xyv = \frac{x}{y} transforms it into a separable form. The key insight is recognizing that when we substitute x=vyx = vy, the terms involving eve^v cancel out, leaving a simple separable equation.

Solution Steps

  1. Step 1: Rewrite the given differential equation as:

    yexydx−xexydy=y2dyy e^{\frac{x}{y}} dx - x e^{\frac{x}{y}} dy = y^2 dy
  2. Step 2: Let v=xyv = \frac{x}{y}, so x=vyx = vy. Differentiating:

    dx=v dy+y dvdx = v \, dy + y \, dv
  3. Step 3: Substitute x=vyx = vy and dx=v dy+y dvdx = v \, dy + y \, dv in the equation:

    yev(v dy+y dv)=(vyev+y2)dyy e^v (v \, dy + y \, dv) = \left(vy e^v + y^2\right) dy
  4. Step 4: Simplify:

    vyevdy+y2evdv=vyevdy+y2dyvy e^v dy + y^2 e^v dv = vy e^v dy + y^2 dy

    The term vyevdyvy e^v dy cancels on both sides.

  5. Step 5: We get:

    y2evdv=y2dyy^2 e^v dv = y^2 dy

    which simplifies to:

    evdv=dye^v dv = dy

    (since y≠0y \neq 0).

  6. Step 6: Integrate both sides:

    ∫evdv=∫dy\int e^v dv = \int dy

    giving:

    ev=y+Ce^v = y + C
  7. Step 7: Substitute back v=xyv = \frac{x}{y} to get the general solution:

    exy=y+Ce^{\frac{x}{y}} = y + C