How do you name a line using two points?

Conditions

• The object being named is a line.
• Two distinct points are chosen on that line.

Reasoning, step by step

1. Identify two points on the line, for example X and Y.
2. Write the letters X and Y together.
3. Place a double-headed arrow over the letters to get $\overleftrightarrow{XY}$.
4. Note that $\overleftrightarrow{YX}$ is also a valid name for the same line.

Example

The instructor draws a line with points X and Y, then writes $\overleftrightarrow{XY}$ and $\overleftrightarrow{YX}$, stating that the order does not matter.

Common misconceptions

• Omitting the double-headed arrow symbol.
• Thinking that the order of the letters changes the line being named.

Watch the explanation

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• How is segment notation different from line notation?