1 Answer

Jklaus · Answer 1 · 2021-12-13T21:16:26+0000

Answer:

$m\angle DEC=91^o$

Explanation:

see the attached figure to better understand the problem

we know that

The measure of the interior angle is the semi-sum of the arcs comprising it and its opposite

so

$m\angle DEC=(1)/(2)[arc\ AB+arc\ DC]$

substitute the given values

$m\angle DEC=(1)/(2)[39^o+143^o]$

$m\angle DEC=(1)/(2)[182^o]$

$m\angle DEC=91^o$

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