Concept:If (x−a) is a factor of a polynomial, then the remainder obtained by dividing the polynomial by (x−a) must be zero.Explanation:Let P(x)=bx−ax+x2.Rewrite it as P(x)=x2+(b−a)x.Divide P(x) by (x−a):x2+(b−a)x=(x−a)(x+b)+abSince (x−a) is a factor, the remainder ab must be 0.Thus, P(x)=(x−a)(x+b).Therefore, the other factor is (x+b).Answer:A. (x+b)