a)
Slope line 1 = (8 + 2)/(7+7) = 10/14 = 5/7
Slope line 2 = (8 + 6)/(-5 - 5) = 14/-10 = -7/5
Slope line 3 = (-3+8)/(0+7) = 5/7
b)
Line 1 and line 3 are parallel (parallel lines have same slopes)
Line 1 and line 2 are perpendicular (perpendicular lines, slope is opposite and reciprocal)