1.已知x+y=5,2x-y=1化简xy(x+y的平方-y的平方(xy-x)+2x(x-y的平方),并求它们的值. 3．3ab-4ab+8ab-7ab+ab=______． 4．7x-(5x-5y)-y=______． 5．23a3bc2-15ab2c+8abc-24a3bc2-8abc=______． 6．-7x...