∵A,B互为相反数,X,Y互为倒数,C=3
∴A+B=0 X*Y=1 C=3
∴1/3C^2(XY)^3-2/3C^2+(A+B)^2-4/3C^2(XY)^3
=1/3*3²*1³-2/3*3²+0²-4/3*3²*1²
=3-6-12
=-15