It is proved that f(x) is continuously derivable in the closed interval [a, b] and the open interval [a, b]. ...

Are you sure you copied the question correctly? Cotb (sin?1) 2 francs (2 pounds)? It doesn't look very harmonious. If you're sure you copied it correctly, I'll try. However, I hope the landlord can provide a word formula editor version of the formula, which feels a bit unreliable. ...