I keep getting “Perpendicular and parallel lines” questions wrong in Straight Lines. What's the trap?
thinking perpendicular lines have equal slopes.
The usual trap: thinking perpendicular lines have equal slopes. How to avoid it: parallel → equal slopes; perpendicular → m₁·m₂ = −1. Go back to the definition — parallel lines have equal slopes; perpendicular lines have slopes whose product is −1.
Key point
Perpendicular and parallel lines
Common mistake
thinking perpendicular lines have equal slopes.
Memory tip
parallel → equal slopes; perpendicular → m₁·m₂ = −1.
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