Concept:Factorizing a quadratic expression means writing it as a product of two binomial factors.Explanation:We need two numbers that multiply to give −15 and add to give −2.Those numbers are −5 and 3, because (−5)(3)=−15 and −5+3=−2.Rewrite the middle term: x2−2x−15=x2−5x+3x−15.Group the terms: (x2−5x)+(3x−15).Factor each group: x(x−5)+3(x−5).Factor out the common bracket: (x−5)(x+3).Answer:(x−5)(x+3), which is option D.