Solve y′′+2y′+y=0y'' + 2y' + y = 0y′′+2y′+y=0.
y=(C1+C2x)e−xy = (C_1 + C_2 x) e^{-x}y=(C1+C2x)e−x
y=C1e−x+C2exy = C_1 e^{-x} + C_2 e^{x}y=C1e−x+C2ex
y=C1cosx+C2sinxy = C_1 \cos x + C_2 \sin xy=C1cosx+C2sinx
y=e−xy = e^{-x}y=e−x