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Couple ∠ ° and ∠ ° and couple ∠ ° and ∠ ° are opposite angles. Moreover, in the image,

∠ ° and ∠ ° are pairs of straight angles, such that:

1. ° + ° = 180°, then ° = 180° − °

2. ° + ° = 180°, then ° = 180° − °

A pair of opposite angles occurs when two lines intersect so that the two angles that are
opposite each other are called opposite angles. The measure of two opposite angles is the same.

Relationship of Angles on Two Parallel Lines

Pay attention to the following table!

Table 1. Relationship of Angles on Two Parallel Lines

No. Figure Note

1. The points K, L, M, and N are interior points
of lines k and l or the points in the inner region

line k and l

2. The points O, P, Q, R, and S are the exterior
points of the lines k and l or the points that are

in the outer region of the lines k and l

3. The line m intersects the lines k and l. The

points K and L with the points M and N are
the points that are opposite each other in the

interior area of the lines k and l.

4. The line m intersects the lines k and l. The
points O and P with the point S are the points

that are opposite each other in the exterior area
of the lines k and l. Likewise, the point R and

the point Q are two points that are opposite

each other in the exterior area of the lines k

and l.

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