ab²-1/2(6ab-8ab²)+3ab a=1/2 b=-2=ab²-3ab+4ab²+3ab=5ab²=5x1/2x(-2)²=5/2x4=10
abb-3ab+4abb+3ab=5abb+0=5abb当a=1/2 b=-2时原式=5*(1/2)*(-2*-2) =5*(1/2)*4 =5*2 =10bb是b的平方1/2是二分之一
