Lines a and b are parallel.
Calculate the size of angle B.
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Lines a and b are parallel.
Calculate the size of angle B.
If one of two corresponding angles is a right angle, then the other angle will also be a right angle.
Alternate interior angles are on opposite sides of the transversal and between the parallel lines. The 100° angle and angle B are on different sides of the diagonal line and both lie between lines a and b.
That would be true if they were corresponding angles (same position relative to each parallel line). But these are alternate interior angles, which are supplementary - they add up to 180°.
Corresponding angles are in the same position at each intersection and are equal. Alternate interior angles are on opposite sides of the transversal, between the parallel lines, and are supplementary (add to 180°).
Since alternate interior angles are supplementary:
Therefore:
Yes! First identify the angle relationship (alternate interior, corresponding, etc.), then apply the correct rule. Each relationship has its own property.
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