Triangle with Three Right Angles

Puzzle

To make a triangle that has $3$ right angles.

Solution

A spherical triangle whose sides are the arcs of great circles which intersect at right angles.

Sources

• 1821: John Jackson: Rational Amusement for Winter Evenings
• 1992: David Wells: Curious and Interesting Puzzles ... (previous) ... (next): Rational Amusements for Winter Evenings: $157$