Question

1. practice: summarizing

use notation and marks to summarize the line relationship.
line leadership
line ab is parallel to cd
notation
___________

Explanation:

Step1: Identify line notation

To represent lines, use $\overleftrightarrow{AB}$ for line AB, $\overleftrightarrow{CD}$ for line CD.

Step2: Use parallel symbol

The standard notation for parallel lines is $\parallel$, so combine to get $\overleftrightarrow{AB} \parallel \overleftrightarrow{CD}$.

Answer:

$\overleftrightarrow{AB} \parallel \overleftrightarrow{CD}$