Prove that, summation of four angles of a quadrilateral is equal to four right angles.

Ex: In the figure, ABC is an equilateral triangle. D, E and the midpoint of AB,BC and AC respectively.            (a) Prove that, summation of four angles of a quadrilaterals equal to four right angles. Prove that, ∠BDF+∠DFE+∠FEB+∠EBD= 4 right angles.      (b) Prove that, DF∥BC and DF = ½ BC. Particular enunciation: Given that, in ...