Chapter 9 - Quadratic Functions and Equations - 9-4 Factoring to Solve Quadratic Equations - Practice and Problem-Solving Exercises - Page 558: 36

The student didn't subtract 20 from both sides before factoring the equation. The student should have had $2x^2+3x-20 = 0$ as the next part of their steps.

$2x^2+3x= 20$ $2x^2+3x-20 = 20-20$ $2x^2+3x-20 = 0$ $2x^2+8x-5x-20 =0$ $2x(x+4)-5(x+4)=0$ $(2x-5)(x+4)=0$ $2x-5=0$ $2x-5+5 = 0+5$ $2x = 5$ $2x/2 = 5/2$ $x = 5/2$ $x+4 = 0$ $x+4-4 = 0-4$ $x = -4$