tanA=1/2
tanB=2/3
∴ tan(A+B)
=(tanA+tanB)/(1-tanAtanB)
=(1/2+2/3)/[1-(1/2)*(2/3)]
=(7/6)/(2/3)
=7/4
∴ tanC=tan[π-(A+B)]=-tan(A+B)=-7/4