Question 604190
assume the equation is y = mx + c


pass through (6,6):
6 = 6m + c
pass through (-6,-6):
-6 = -6m + c


use elimination procedure:
 6 =  6m + c
-6 = -6m + c
------------- (-)
12 = 12m
m = 12/12 = 1


6 = 6m + c
6 = 6*1 + c
6 = 6 + c
6 - 6 = c
0 = c


so the line equation for the problem is y = x