a+b=6,ab=27/4,a>b,a²×b-b等于多少a,b是方程x²-6x+27/4=0,即4x²-24x+27=(2x-3)(2x-9)=0的二根,故a=9/2,b=3/2.∴a²b-b=(a²-1)b=(81/4-1)×(3/2)=(77/4)×(3/2)=231/8