ACT Preparation / Unit 13 ACT 1204 short lesson, about 20 seconds
Alternate Interior Angles
Captions available
The idea
When a transversal crosses two parallel lines, alternate interior angles, on opposite sides of the transversal and between the parallels, are equal.
In practice
If one interior angle at the upper line is 65°, the alternate one at the lower line is 65°.
Where people slip
The rule needs parallel lines. Some books mark this pair with a Z shape, a memory aid only.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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