What are parallel lines?
- Parallel lines are equidistant meaning they never meet
- Parallel lines have equal gradients
What are perpendicular lines?
- Perpendicular lines meet at right angles
- The product of their gradients is -1
What are collinear lines?
- Collinear lines are two line segments that are part of the same line
- They have equal gradients and pass through, or meet at, a point
- Rearrange their equations into the same form and they will be identical
How do I tell if lines are parallel or perpendicular?
- Rearrange equations into the form y = mx + c
- m is the gradient
- Exam questions are good at “hiding” parallel and perpendicular lines.
- For example a tangent and a radius are perpendicular.
- Parallel lines could be implied by phrases like “… at the same rate …”