14. (2023春•招远市校级期中)在ΔABC\Delta ABCΔABC中,已知cosA=45\cos A=\frac{4}{5}cosA=54,tanB=12\tan B=\frac{1}{2}tanB=21,则tan(A−C)=(\tan (A-C)=(tan(A−C)=( )))