Question
In the given figure, $\triangle\text{ABC}$ is equilateral. Find
  1. $\angle\text{BDC}$
  2. $\angle\text{BEC}$

Answer

  1. Given: $\triangle\text{ABC}$ is an equilateral triangle
i.e., each of its angle = 60°

$\Rightarrow\ \angle\text{BAC}=\angle\text{ABC}=\angle\text{ACB}=60^\circ$

Angles in the same segment of a circle are equal.

$\text{i.e.},\angle\text{BDC}=\angle\text{BAC}=60^\circ$

$\therefore\ \angle\text{BDC}=60^\circ$
  1. The opposite angles of a cyclic quadrilateral are supplementary.
Then in cyclic quadrilateral ABEC, we have:

$\angle\text{BAC}+\angle\text{BEC}=180^\circ$

$\Rightarrow\ 60^\circ+\angle\text{BEC}=180^\circ$

$\Rightarrow\ \angle\text{BEC}=(180^\circ-60^\circ)=120^\circ$

$\therefore\ \angle\text{BDC}=60^\circ$ and $\angle\text{BEC}=120^\circ$

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