Which of the following differential equations is non-linear?
y′+3y=exy' + 3y = e^xy′+3y=ex
y′′+4y′+y=0y'' + 4y' + y = 0y′′+4y′+y=0
y′+y2=xy' + y^2 = xy′+y2=x
y′+sin(x)y=0y' + \sin(x)y = 0y′+sin(x)y=0