sphere

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The normal, or perpendicular, at each point of a surface defines the corresponding tangent plane, and vice versa.

sphere with circumscribing cylinder

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Estimated battle casualties, Normandy invasion, World War II. WWII, D-Day

Estimated Battle Casualties During the Normandy Invasion and Campaign to Liberate Paris (June–August 1944)

Paul Revere. "The bloody massacre perpetrated in King Street Boston on March 5th 1770 by a party of the 29th Regt.," engraved by Paul Revere. Boston Massacre.

There’s a Riot Goin’ On: Riots in U.S. History (Part One)

Salem Witch Trials. Photogravure after the painting by Walter McEwen titled - The Witches - circa 1890s.

How Rye Bread May Have Caused the Salem Witch Trials

Statue of Nostradamus

Nostradamus and His Prophecies

Demystified - Do Lemmings Really Commit Mass Suicide? illustration

Do Lemmings Really Commit Mass Suicide?

airplane in flight (plane, aircraft, flying)

7 Puzzling Plane Disappearances

Time zone map with standard time zones and International Date Line

Why Are Some Time Zones 30 Minutes Off Instead of an Hour?

sphere: Related Content

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Photos

The normal, or perpendicular, at each point of a surface defines the corresponding tangent plane, and vice versa.

sphere with circumscribing cylinder

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Topics

Poincaré conjecture Ewald’s sphere spherical triangle pseudosphere geodesic rhumb line ellipsoid cone paraboloid hyperboloid cylinder

Key People

Archimedes

Archimedes

Greek mathematician

Menelaus of Alexandria

Greek mathematician

Quiz

Equations written on blackboard

Numbers and Mathematics