If the line passing through the points (a, 1) and (5, 7) is parallel to the line passing through the points (8, 8) and (a + 2, 1), what is the value of a?
a =?
since the slopes are the same,
6/(5-a) = -7/(a+2-8)
6(a-6) = 7(a-5)
6a-36 = 7a-35
a = -1