Learn the 2 Rules
1Vertically opposite angles are equal.
The angles facing each other across the X are identical twins.
2Neighbours total 180°.
Angles next to each other in the X sit on a straight line.
3One angle unlocks all four.
Know 50°? Opposite is 50°; the other pair are 180 − 50 = 130° each.
Worked Example
Two lines cross. One angle is 74°. Find the other three.
Watch Out! Common Mistakes
Wrong pair! Only opposite angles are equal. Neighbours total 180°: 74° and 106°.
Naming trap! Vertically opposite = sharing a vertex. The rule works whatever way the X is tilted.
Check! The four angles at the crossing always total 360°. 74+106+74+106 = 360 ✓ — use it to verify.
⬇ Cheat Sheet
- Two crossing lines make 2 pairs of equal (vertically opposite) angles.
- Neighbouring angles total 180°.
- One known angle reveals all four.
- All four together total 360°.
📖 Continue Your Journey
Quick summary
- Vertically opposite angles (across the X) are equal.
- Neighbouring angles at the crossing total 180°.
- One known angle determines all four: 74° → 74°, 106°, 74°, 106°.
- 'Vertically' refers to the shared vertex, not to being upright.
Frequently asked questions
What are vertically opposite angles?
The pairs of angles facing each other when two straight lines cross. Each pair is equal — and the name comes from the shared vertex, not from being vertical.
If one angle at a crossing is 74°, what are the others?
The opposite angle is 74°, and the two neighbours are each 180 − 74 = 106°.
How can children check their four answers?
Add them: the four angles around the crossing point must total 360°.
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