What is the solution to the differential equation y' = y^2 - 1?

Practice Questions

Q1
What is the solution to the differential equation y' = y^2 - 1?
  1. y = tan(x + C)
  2. y = 1/(C - x)
  3. y = C/(1 - Cx)
  4. y = C/(x - 1)

Questions & Step-by-Step Solutions

What is the solution to the differential equation y' = y^2 - 1?
  • Step 1: Start with the differential equation y' = y^2 - 1.
  • Step 2: Rewrite y' as dy/dx, so the equation becomes dy/dx = y^2 - 1.
  • Step 3: Separate the variables by moving all y terms to one side and x terms to the other side: dy / (y^2 - 1) = dx.
  • Step 4: Factor the left side: dy / ((y - 1)(y + 1)) = dx.
  • Step 5: Integrate both sides. The left side requires partial fraction decomposition: 1/((y - 1)(y + 1)) = A/(y - 1) + B/(y + 1).
  • Step 6: Solve for A and B to find the integral: ∫(1/(y - 1) - 1/(y + 1)) dy = ∫dx.
  • Step 7: The integrals give ln|y - 1| - ln|y + 1| = x + C, where C is the constant of integration.
  • Step 8: Combine the logarithms: ln|(y - 1)/(y + 1)| = x + C.
  • Step 9: Exponentiate both sides to eliminate the logarithm: (y - 1)/(y + 1) = e^(x + C).
  • Step 10: Let K = e^C, then (y - 1)/(y + 1) = Ke^x.
  • Step 11: Solve for y: y - 1 = Ke^x(y + 1).
  • Step 12: Rearrange to isolate y: y(1 + Ke^x) = 1 + Ke^x.
  • Step 13: Finally, solve for y: y = (1 + Ke^x) / (1 + Ke^x).
  • Step 14: This simplifies to y = 1/(C - x), where C is a constant.
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