Question 1037268
<pre><b>
His way will work, but it's much longer, and that's not 
the way you were taught to find the angle between two lines.

You find the slopes of AB and BC, m<sub>1</sub> and m<sub>2</sub>,

then you use the formula for the acute angle between two lines:

{{{tan(theta)}}}{{{""=""}}}{{{abs((m[1]-m[2])/(1+m[1]m[2]))}}}

then find the inverse tangent.

From the looks of the graph, the angle you want ABC is obtuse so
you find the acute angle between AB and BC and then find its
supplement, which means you will subtract from 180°.

Answer: 108.4349488°

Edwin</pre></b>