∫dx/(ex + 4e-x) = f (x) + c then f (x) is equal to

∫dx/(e^x + 4e^-x)

^{=∫exdx/(ex2 + 4)}  

^{=1/2∫2exdx/(ex2 + 4)}

^{=1/2 log [ex2 + 4]+c}

^therefore,

^fx= 1/2 log [e^x2 + 4]

plz approve if u like..