# Parallel lines

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::::::::::::::::::PARALLEL LINES:::::::::::::::::::::::

Parallel lines (II) are COPLANAR lines that DON’T INTERSECT

Skew lines are NONCOPLANAR lines, they’re NEITHERPARALLEL NOT INTERSECTING

If 2 lines are cut by a third plane, then the lines of intersection are PARALLEL.

A TRANSVERSAL is a line that intersects 2 or more COPLANAR LINES inDIFFERENT points.

ALTERNATE INTERIOR ANGLES are two NONADJACENT interior angles on OPPOSITE SIDE of the transversal.

SAME SIDE INTERIOR ANGLES are two interior angles on the SAMESIDE of the transversal.

CORRESPONDING ANGLES are two angles in CORRESPONDING positions ELATIVE to the two lines.

::::::ANGLES IN PARALLEL LINES::::::::::

If 2 PARALLELLINES are cut by a TRANSVERSAL, then CORRESPONDIING ANGLES are CONGRUENT.

If 2 PARALLEL LINES are cut by a transversal, then ALTERNATE INTERIOR ANGLES are CONGRUENT.

If 2PARALLEL LINES are cut by a transversal, then SAME SIDE INTERIOR ANGLES are SUPPLEMENTARY.

If a TRANSVERSAL is PERPENDICULAR to one of the 2 PARALLEL LINES, then it is PERPENDICULARto the other one.

:::::::::::PROVING LINES PARALLEL::::::::::::::::::::

If two PARALLEL LINES are cut by a transversal, then CORRESPONDING ANGLES are CONGRUENT.

If twolines are CUT by a TRANSVERSAL and ALTERNATE INTERIOR ANGLES are congruent, then the lines are PARALLEL.

If two lines are cut by a transversal and SAME SIDE INTERIOR ANGLES aresupplementary then the lines are PARALLEL.

In a PLANE two lines PERPENDICULAR to the SAME LINE are PARALLEL.

Through a POINT OUTSIDE A LINE, there is exactly ONE LINE PARALLELto the given line.
Through a POINT OUTSIDE A LINE, there is exactly ONE LINE PERPENDICULAR to the given line.

Two lines are PARALLEL to a THIRD line are PARALLEL to each other.