多项式A为:5y^2 +4y-9 -(3y^2 -7y+1)
=(5y^2-3y^2)+(4y+7y)-9-1
=2y^2 +11y -10
正确解为:2y^2 +11y -10 -(3y^2 -7y+1)
=(2y^2-3y^2)+(11y+7y)-10-1
=-y^2 +18y -11
希望采纳