ab-3b=-75(ab-3b)=-355ab-15b=-35
-35
5ab-15b=5(ab-3b)=5*(-7)=-35
ab-3b+7=0同时乘以5得:5ab-15b+35=0所以:5ab-15b=-35
ab-3b+7=0同时乘以5得:5ab-15b+35=0得:5ab-15b=-35