Parallel lines are distinct lines (in the same plane) that never intersect (never cross each other).

The slope of a line measures its steepness (or its angle from the horizontal).
Lines that are parallel have the same steepness (or the same angle).

Parallel lines have the same slope!

Parallel lines are marked with "feathers" (similar to what you see on an archery arrow) to show that they are parallel. The "feathers" look like "greater than" symbols on the lines.

Equations of Lines: y = 2x + 1 y = 2x - 5 y = 2x + 1.3
y = 2x

All of the lines at the left are parallel.
They all have the same slope (m).
(y = mx + b)

Perpendicular lines are lines that intersect at a right angle.

Perpendicular lines have negative reciprocal slopes!

Perpendicular lines are marked with "a box" to indicate the location of the right angle.
Perpendicular lines intersect in one location, which becomes the vertex of the right angle.
Remember that a right angle contains 90ยบ (think of the angle in the corner of a square).

To find the negative reciprocal of a number,
flip the number over (take the reciprocal, invert)
and negate that value.

Number:

Negative Reciprocal:

3

Equations of Lines: y = 2x + 1

These lines are perpendicular since their slopes are negative reciprocals.
The negative reciprocal of 2 is .

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