Brainlag PlusParallel lines share a gradient; perpendicular gradients multiply to −1. Use both to find equations, including perpendicular bisectors.
Same gradient, or the negative reciprocal
Parallel lines have the same gradient: y = 3x + 1 and y = 3x − 4 never meet.
Perpendicular lines meet at a right angle, and their gradients multiply to −1. To find the perpendicular gradient, flip the fraction and change the sign: the negative reciprocal.
- gradient 3 = 3/1: perpendicular −1/3
- gradient −2/5: perpendicular 5/2
- check: −2/5 × 5/2 = −1
y = 2x and y = −x/2 + 1: 2 × (−1/2) = −1, so they cross at a right angle.
The rest of this lesson and its 7 practice questions are in Plus.
Screen 1 of 4, free to read.
- 7 exam-style questions, marked as you go, each with a worked solution
- The Graphing Calculator beside every question
- Anything you get wrong is saved to your flashcards