we have the following set of equations,
We need them in slope-intercept form, therefore,
Line 1)
Line 2)
Line 3)
Perpendicular lines have slopes that are negative reciprocals of one another
Notice that the slope of Line 1, m1= -2, is the negative reciprocal of the slop of Line 2, m2= 1/2
Line 3 in not parallel, nor perpendicular to any line
Answer: Line 1 and Line 2 are perpendicular, but Line 3 is neither parallel nor perpendicular to any one.