Gonio: Angle Puzzle

One angle carries a question mark. Chase it through the figure with the rules you already know. No ads, no account, works offline.

One angle in the figure is marked with a question mark. Chase it.

Not a calculator, not a worksheet — a chase. Each step you take opens the next one, until the marked angle has nowhere left to hide.

HOW TO PLAY

• Look for an angle you can settle right now from the values already on the figure
• Apply one rule: angles in a triangle make 180, angles on a straight line make 180, vertical angles are equal, parallel lines give equal corresponding and alternate angles, the base angles of an isosceles triangle match
• Write that value in and it becomes ammunition for the next step
• Keep going until the question mark falls

EVERY PUZZLE IS FULLY DETERMINED Each figure is generated and then run through a solver that propagates the rules from the marked values. A puzzle ships only if the target angle is completely pinned down, so the numbers on screen are always enough. No guessing, no measuring, no puzzle that turns out to be underspecified.

FIGURES ARE NOT DRAWN TO SCALE Layout is chosen so every label stays readable, not so a protractor would agree. A corner is a right angle only when it carries the small square mark, and two sides are equal only when they carry matching ticks. That is the same convention every geometry book uses, and it is what keeps the puzzles honest.

DIFFICULTY THAT IS MEASURED, NOT GUESSED Rated from the chase itself: how many deduction steps the shortest chain needs, which rules it forces you to reach for, and whether the figure can be cracked one angle at a time or holds out until several are combined. Four levels, from a gentle start to genuinely hard.

STUCK A hint points at the rule to use next and the angle it settles, so you learn the move rather than being handed the answer. You earn a hint for every four puzzles you solve.

BUILT TO BE QUIET No ads. No account. No sign-up. No tracking. Nothing is sent anywhere — the whole game runs on your device and works in aeroplane mode.

GONIO PRO Unlimited hints and every puzzle. Available as a weekly or yearly subscription, or as a one-time lifetime purchase.

Subscriptions renew automatically at the price shown in the app unless cancelled at least 24 hours before the end of the current period. Payment is charged to your Apple Account on confirmation. You can manage or cancel in your Apple Account settings; deleting the app does not cancel a subscription.

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