All of these transformations are equivalent to reflection across the line y=x:
- a reflection across the y-axis followed by a clockwise rotation 90° about the origin
- a clockwise rotation 90° about the origin followed by a reflection across the x-axis
- a counter-clockwise rotation 90° about the origin followed by a reflection across the y-axis
- a reflection across the x-axis followed by a counter-clockwise rotation 90° about the origin
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These are all but the second choice.
... reflection across y: (x, y) ⇒ (-x, y); 90°CW: (-x, y) ⇒ (y, x)
... 90°CW: (x, y) ⇒ (y, -x); reflection across x: (y, -x) ⇒ (y, x)
... 90°CCW: (x, y) ⇒ (-y, x); reflection across y: (-y, x) ⇒ (y, x)
... reflection across x: (x, y) ⇒ (x, -y); 90°CCW: (x, -y) ⇒ (y, x)
Note that the second choice gives a different result:
... reflection across y: (x, y) ⇒ (-x, y); 90°CCW: (-x, y) ⇒ (-y, -x)
