English: Left panel shows stability region ${\displaystyle S\subset ℂ}$ of the explicit Euler method. The method is stable for ${\displaystyle h\lambda }$ inside the green disk. Right panel shows (the complement of) the stability region of the implicit Euler method. The method is stable for ${\displaystyle h\lambda }$ outside the red disk. The method is A-stable, since ${\displaystyle S\supset {ℂ}^{-}}$.