Right Triangle -- from Wolfram MathWorld

Right Triangle -- from Wolfram MathWorld

Altitude -- from Wolfram MathWorld

Second Neuberg Triangle -- from Wolfram MathWorld

Right Triangle -- from Wolfram MathWorld

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Reuleaux Triangle -- from Wolfram MathWorld

Napoleon's theorem - Wikipedia

Emily Fulcher. “According to MathWorld, trigonometry is the study

Diophantine equation - Wikipedia