若3的x次方=4，3的y次方=6，求9的2x-y次方的值9的2x-y次方=3的4x-2y次方=3的4x次方/3的2y次方=4^4/6^2=256/36=64/9
9^(2X-Y)+27^(X-Y)=3^2(2X-Y)+[3^(X-Y)]^3=(3^4X)/(3^2Y)+(4/6)^3=4^4/6^2+(2/3)^3=256/36+8/27=192/27+8/27=200/27
