Question 1065932
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<pre>
The angle ACD is the exterior angle of the triangle ABC at bertx C.

The exterior angle of any triangle is the sum of the two other angles of the triangle:

m(ACD) = m(A) + m(B) = 53 + 84 degrees.
</pre>


See the lesson

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=http://www.algebra.com/algebra/homework/Triangles/Sum-of-the-interior-angles-of-a-triangle.lesson>Sum of the interior angles of a triangle</A>

in this site.


Also, &nbsp;you have this free of charge online textbook on Geometry

&nbsp;&nbsp;&nbsp;&nbsp;<A HREF=https://www.algebra.com/algebra/homework/Triangles/GEOMETRY-your-online-textbook.lesson>GEOMETRY - YOUR ONLINE TEXTBOOK</A> 

in this site.


The referred lesson is the part if this textbook under the topic "<U>Properties of triangles</U>".