Question

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Answer 1

the slopes will be the same for parallel lines, negative reciprocals for perpendicular lines, neither of these for neither parallel nor perpendicular.
also, 2 vertical lines are parallel. a vertical line is perpendicular to a horizontal line.

Answer 2

if lines are parallel, they have the same gradients/slopes and perpendicular lines have the product of their gradients to be -1

Answer 3

or graph them and look in this case