Question 1156399

 If the length of a rectangle is 7 meters less than twice the width, we have
L=2W-7
If the area is 60 square meters, we have 
L×W=60 substitute L
(2W-7)×W=60
2W^2-7W=60
2W^2-7W-60=0
2W^2-15W+8W-60=0
(2W^2+8W)-(15W-60)=0
2W(W+4)-15(W+4)=0
(W+4)(2W-15)=0
2W-15=0 W=15/2 W=7.5 
Can someone explain where the 15 and 8 came from?
<pre>{{{matrix(1,3, 2W^2 - 7W - 60, "=", 0)}}} 
{{{matrix(1,3, 2W^2 - 15W + 8W - 60, "=", 0)}}} <b> <===== I guess you're referring to the - 15 and + 8 here</b>
The - 15W + 8W REPLACES - 7W since - 15W + 8W = - 7W
The - 15 and + 8 were derived from the NEED to find 2 factors with a product of "ac," or + 2 * - 60 = - 120, and simultaneously SUM to - 7. 
These 2 factors are: - 15 and + 8 (notice that the factors have OPPOSITE signs!).