Videos
https://tutors.com/math-tutors/geometry-help/proving-lines-are-parallel
https://www.youtube.com/watch?v=Lm9-NzG6RBY
https://www.youtube.com/watch?v=92gT6vHtEXc
https://www.youtube.com/watch?v=84OU8SK0Rzc
https://www.youtube.com/watch?v=lSKalGqeBIM
https://www.youtube.com/watch?v=aTGOfPo8Pxg
Practice Activities & Worksheets
https://www.math.uh.edu/~jac/FA16M1312/CourseNotes/Blank/1312_Day6_sect2.3.pdf
https://mryangteacher.weebly.com/uploads/7/7/0/2/7702250/proving_lines_parallel_notes_and_key.pdf
https://www.ck12.org/book/ck-12-geometry-second-edition/section/3.3/
https://cdn.kutasoftware.com/Worksheets/Geo/3-Proving%20Lines%20Parallel.pdf