| ❌ Wrong | ✅ Correct | | :--- | :--- | | Forgetting negative signs in rotation | Memorize: ( 90^\circ ) CCW: ( (-y, x) ) | | Mixing reflection over ( y=x ) and ( y=-x ) | ( y=x ) swaps; ( y=-x ) swaps and negates | | Adding translation vector incorrectly | ( x' = x + a ), not ( x' = a - x ) | | Using ( k ) as fraction incorrectly | ( k=1/2 ) reduces size, not enlarges |
He turned the dials to 1-5. Click!
| ❌ Wrong | ✅ Correct | | :--- | :--- | | Forgetting negative signs in rotation | Memorize: ( 90^\circ ) CCW: ( (-y, x) ) | | Mixing reflection over ( y=x ) and ( y=-x ) | ( y=x ) swaps; ( y=-x ) swaps and negates | | Adding translation vector incorrectly | ( x' = x + a ), not ( x' = a - x ) | | Using ( k ) as fraction incorrectly | ( k=1/2 ) reduces size, not enlarges |
He turned the dials to 1-5. Click!