Chapter 9 - Quadratic Functions and Equations - 9-6 The Quadratic Formula and the Discriminant - Practice and Problem-Solving Exercises - Page 572: 42

$x = 2.425$ inches

$7*5=35$ $35*2 = 70$ $70 = (x+7)(x+5)$ $70 = x^2+7x+5x+35$ $x^2+12x+35 =70$ $x^2+12x+35-70 = 70-70$ $x^2+12x-35=0$ $x= (-b±\sqrt {b^2-4ac})/2a$ $x= (-12±\sqrt {12^2-4*1*-35})/2*1$ $x= (-12±\sqrt {144+140})/2$ $x= (-12±\sqrt {284})/2$ $x= (-12±16.85)/2$ $x= (-12+16.85)/2$ $x=4.85/2 = 2.425$ $x= (-12-16.85)/2$ $x= -28.85/2 =-14.425$ (we can't have a negative length)