The first trap is the sneakiest, because two of the three rules say "equal" — so it's easy to assume the third does too. It doesn't.
Co-interior Angles Are Not Equal
Corresponding (F) and alternate (Z) angles are equal — copy the number straight across. But co-interior angles (C) are different beasts: they add to 180°. If one is 70°, its co-interior partner is 180 − 70 = 110°, not another 70°. They only match if both happen to be 90°. Any other time, treating them as equal gives the wrong answer.
The Rules Need Parallel Lines
The second trap: all three rules only work when the two lines are parallel. Slide the switch in the toy to tip one line out of parallel, and watch the two "co-interior" angles stop summing to 180° — the rule simply collapses. So before you use any of these rules, check the diagram for the matching arrows that mark the lines parallel. No arrows (and no statement that they're parallel) means no rules.
Naming the Right Pair
The last trap is mixing up which pair you're looking at. Two equal-looking angles might be alternate (Z) or corresponding (F) — the rule is the same (equal), but the reason you write down has to match the shape. And a C-shape must never be called alternate. Use the quiz in the toy to drill the shapes until F, Z and C are instant.
Why the Reason Matters
In NSW exams you're marked on the justification, not just the number. Writing "x = 110° (co-interior angles, parallel lines)" earns the reasoning mark; writing only "110°" can leave marks on the table even when the number's right. Name the pair, name the rule, name the parallel condition — every time.