Parallel and perpendicular lines
Objective. Use gradients to identify parallel and perpendicular lines.
- 1. Learn
- 2. Worked example
- 3. Practice
- 4. Feedback
- 5. Continue
Learn: the key idea
Parallel lines share a gradient. Perpendicular gradients multiply to −1, so the perpendicular gradient is the negative reciprocal.
Worked example
Find a line perpendicular to y = 2x + 1 through (0, 4).
- 1Gradient 2, so perpendicular gradient is −1/2.
- 2Intercept is 4.
- 3y = −x/2 + 4.
Answer: y = −0.5x + 4
Concept mastery
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Practice
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Start practisingCommon mistake. Using the reciprocal without changing the sign.
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