This key facts covers Parallel Lines within Parallel & Perpendicular for GCSE Mathematics. Revise Parallel & Perpendicular in Graphs for GCSE Mathematics with 14 exam-style questions and 12 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 2 of 10 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
Parallel Lines
- Definition: Lines that never meet (same direction)
- Key Property: Same gradient
- Different y-intercepts: Otherwise they would be the same line
- Symbol: || (e.g., L₁ || L₂)
- Distance: Constant distance apart everywhere
Practice questions for Parallel & Perpendicular
Which of the following is true about two parallel straight lines?
Explain why a horizontal line and a vertical line are always perpendicular to each other. Your explanation must refer to gradients.
Quick recall flashcards
What is the gradient rule for perpendicular lines?
Perpendicular lines have gradients that multiply to -1. If L1 perp L2 then m1 x m2 = -1.
What is the gradient rule for parallel lines?
Parallel lines have equal gradients. If L1 has gradient m1 and L2 has gradient m2, then L1 || L2 means m1 = m2.