Differential Equations › Section C · Second order differential equations › Topic C.3

Complex roots

When the characteristic equation has no real roots, the solutions oscillate. Euler's formula turns a pair of complex exponentials into real sines and cosines, and the real part of the root decides whether the oscillation fades, grows or holds steady.

In this topic

  • When the discriminant is negative
  • Euler's formula
  • From complex to real solutions
  • Using the formula
  • Worked example: a growing oscillation
  • Worked example: conditions away from zero
  • Reading the solution
  • Common mistakes to avoid
  • Key takeaways

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