Catch a Star

Geometry Level 1

Find D A C + E B D + A C E + B D A + C E B \angle DAC + \angle EBD + \angle ACE + \angle BDA + \angle CEB

Give you answer in degrees.


The answer is 180.

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2 solutions

Siddharth Singh
Nov 29, 2014

Sum of the the exterior angles of every polygon is 360. sum of the exterior angles of then interior pentagon is 360. If we extend each side of the pentagon in the same direction then the sum of all the exterior angles will be 360. And also if we extend the each side in opposite direction then again sum of eterior angles will be 360. Adding both sums 360+360=720 sum of all the outer triangles 5*180=900 THEN SUM OF THE GIVEN ANGLES WILL BE 900-720=180.

Anatoliy Razin
Nov 29, 2014

Let's mark intersection points between A A and C C as P P and Q Q ( B E A C = P BE \cap AC = P and B D A C = Q BD \cap AC = Q ). Then B P Q = C + E \angle BPQ = \angle C + \angle E and B Q P = A + D \angle BQP = \angle A + \angle D

Therefore the sum of angles in a star equals to the sum of angles in a triangle:

A + B + C + D + E = B + P + Q = 180 \angle A + \angle B + \angle C + \angle D + \angle E = \angle B + \angle P + \angle Q = \boxed{180}

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