GraphsKey Facts

Parallel Lines

Part of Parallel & Perpendicular — GCSE Mathematics

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 9 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.

Topic position

Section 2 of 9

Practice

14 questions

Recall

12 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

Keep building this topic

Read this section alongside the surrounding pages in Parallel & Perpendicular. That gives you the full topic sequence instead of a single isolated revision point.

Train Tracks and Right Angles Perpendicular Lines Parallel and Perpendicular Lines The Gradient Rules

Practice Questions for Parallel & Perpendicular

Which of the following is true about two parallel straight lines?

A. They have the same gradient but different y-intercepts
B. Their gradients multiply to give -1
C. They have the same gradient and the same y-intercept
D. One gradient is the negative of the other

1 markfoundation

Explain why a horizontal line and a vertical line are always perpendicular to each other. Your explanation must refer to gradients.

2 marksstandard

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.

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Train Tracks and Right Angles

Perpendicular Lines