由题意,y=(x1-2x2)(2x1-x2)=2x1²-x1x2-4x1x2+2x2²=2(x1+x2)²-9x1x2因为x1,x2是x²-kx+k-1=0的实数根,所以:x1+x2=kx1x2=k-1所以y=2k²-9(k-1)=2k²-9k+9=2(k-9/4)²+9-2*81/16=2(k-9/...