### Possible Answer

80° + 100° + 90° + 90° = 360°. A Square adds up to 360°. Let's tilt a line by 10° ... still adds up to 360°! The Interior Angles of a Quadrilateral add up to 360° ... - read more

(Also see this on Interactive Quadrilaterals). Properties. Four sides (edges); Four vertices (corners); The interior angles add up to 360 degrees: Quadrilateral ... - read more

Please vote if the answer you were given helped you or not, thats the best way to improve our algorithm. You can also submit an answer or search documents about why does a quadrilateral add up to 360 degrees.