Angles in parallel lines · Grade 10
In Grade 10 you learn: angle proofs.
When a straight line (a transversal) crosses two parallel lines, it makes the same angles at each crossing. Corresponding, alternate and co-interior angles let you move angles from one crossing to the other.
Key facts
- Corresponding angles (F shape) are equal.
- Alternate angles (Z shape) are equal.
- Co-interior angles (C shape) add up to 180°.
- At each crossing, vertically opposite angles are equal and neighbouring angles add to 180°.
- Arrows on lines show that they are parallel.
Worked examples
Example 1
A line crosses two parallel lines. One of the angles between them is 112°. Find x.
Answer: x = 68°