Given,
g(x)=∫x4π(f′(t)sect+tantsectf(t))dt
⇒g(x)=∫x4πd(f(t)⋅sect)⇒g(x)=[f(t)sect]x4π
g(x)=f(4π)sec4π−f(x)⋅secx
g(x)=2−f(x)secx=2−(cosxf(x))
Now taking limit both side, we get
x→(2π)−limg(x)=2−x→(2π)−lim(cosxf(x))
Using L'Hospital Rule
=2−x→(2π)−lim(−sinx)f′(x)
=2+sin2πf′(2π)=2+11=3