What is the measure of $\angle ACD$ if the given triangle is an equilateral triangle?

$( A).\ 60^{\circ}$
$( B).\ 120^{\circ}$
$( C).\ 180^{\circ}$
$( D).\ 90^{\circ}$

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Given: In the given figure $\vartriangle ABC$ is an equilateral triangle.

To do: To find the measure of $\angle ACD$

Solution:
 

If $\vartriangle ABC$ is an equilateral triangle, then

$\angle ABC=\angle BCA=\angle CAB=60^{\circ}$

Therefore, $\angle ACD=180^{\circ}-60^{\circ}=120^{\circ}$  [supplementary angles]

Thus, option $(B)$ is correct.

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Updated on: 10-Oct-2022

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