Find the integrating factor μ(x)\mu(x)μ(x) for the linear ODE y′+tan(x)y=sec(x)y' + \tan(x)y = \sec(x)y′+tan(x)y=sec(x).
sin(x)\sin(x)sin(x)
cos(x)\cos(x)cos(x)
sec(x)\sec(x)sec(x)
etan(x)e^{\tan(x)}etan(x)