October 1, 2006
|Space is flat if the three angles of any triangle add up to 180°. For example, Earth's surface is a positively curved two-dimensional space. When you go from the North Pole to Ecuador to Congo and back to the North Pole, you make a triangle whose angles add up to about 270°. All other triangles on this spherical surface also give more than 180°. A saddle-shape surface is negatively curved. Draw a triangle on it, and the angles will sum to less than 180°.|
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