Chapter 3 - Exponents, Polynomials and Functions - 3.4 Factoring Polynomials - 3.4 Exercises - Page 271: 41

$(x-3)(2x-7)$

In the second line of the student's solution, since the parenthesis is preceeded by a minus sign then $21$ should become $-21.$ The correct solution is as follows: \begin{array}{l}\require{cancel} 2x^2-13x+21 \\\\= 2x^2-6x-7x+21 \\\\= (2x^2-6x)-(7x-21) \\\\= 2x(x-3)-7(x-3) \\\\= (x-3)(2x-7) .\end{array}