Straight Angle -- from Wolfram MathWorld

A straight angle is an angle equal to 180 degrees=pi radians. Two right angles make a straight angle, and two straight angles make a full angle.

Wolfram Precalculus Course Assistant on the App Store

Great circle - Wikipedia

Wolfram, Alpha Meets MathWorld—Wolfram

Subtend -- from Wolfram MathWorld

Solved Problem 3. Consider the Great Pyramid of Giza. The

Perpendicular -- from Wolfram MathWorld

Central Angle -- from Wolfram MathWorld

Spherical Coordinates - Intel Community

Trigonometry -- from Wolfram MathWorld

Trigonometry, Part 1 - David The Maths Tutor