Question

For two parallel lines sum of interior angles on the same side of a transversal line is:

Answer 1

Answer:

When a transversal intersects two lines, the two lines are parallel if and only if interior angles on the same side of the transversal and exterior angles on the same side of the transversal are supplementary (sum to 180°).

Answer 2

If the transversal cuts across parallel lines (the usual case) then the interior angles are supplementary (add to 180°). So in the figure above, as you move points A or B, the two interior angles shown always add to 180°.

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