What is the measurement of the blue angle in degrees?
This is part of the series: " It's easy, believe me! "
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At first we can find out that ∠ A B F = 6 0 o in many ways, and this means that A B ≅ A C (As result of its similarity with any half equilateral triangle). Then, we know that △ A B C is isosceles ⇒ ∠ D B C = 1 5 o . As the line segment F C is an altitude and at once a median, we can notice that △ D B C is, too, isosceles, so we have: ( B C ≅ D C ∧ ∠ E D C = 7 5 o ) ⇒ △ E D C ≅ △ A B C ⇒ ∠ D E C = 3 0 o And, by using the exterior angle theorem in tiangles △ E D C and △ D B C we find: x = 9 0 o + 4 5 o = 1 3 5 o