One move, two subjects
The same problem twice
These pairs look nothing alike. They are the same move. Seeing that once is worth more than working either of them again, because what you learn is the move, and the move is what turns up next time in a form nobody warned you about.
Power of a complex number with De Moivre's theoremandFirst order linear equation with an integrating factor
Complex Numbers and Differential Equations . Different subjects entirely.
Eigenvalues and eigenvectorsandSecond order equation with constant coefficients
Linear Algebra and Differential Equations . Different subjects entirely.