Which of the following equations is both linear and first-order?
(y′)2+y=0(y')^2 + y = 0(y′)2+y=0
y′+xy=sin(x)y' + x y = \sin(x)y′+xy=sin(x)
y′′+3y=0y'' + 3y = 0y′′+3y=0
y′+y2=xy' + y^2 = xy′+y2=x