Question 400143
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Hi, 
Line segment AC is a diagonal of 'regular pentagon' ABCDE. What is the measure of angle ACD
Yes! [(180)(n-2)/n], the measure of each interior angle is 108 degrees
Note Editing: diagramming of the particulars/with explanation
 &#8736;B = 108° &#916;ABC Isoseles (&#8736;BAC =&#8736;ACB = 36°) &#8736; ACD = 108°-36° = 72° 
{{{drawing(300,300,-1.1,1.1,-1.1,1.1,
line(-cos(3pi/10),-sin(3pi/10),cos(3pi/10),-sin(3pi/10)),
line(cos(3pi/10),-sin(3pi/10),cos(pi/10),sin(pi/10)),
line(cos(pi/10),sin(pi/10),0,1),  line(0,1,-cos(pi/10),sin(pi/10)), locate(-1.03,.35,B), locate(0,1.1,C), green(line(0,1,-cos(3pi/10),-sin(3pi/10))),line(-cos(pi/10),sin(pi/10),-cos(3pi/10),-sin(3pi/10)), locate(cos(pi/10),sin(pi/10)-.03,D),locate(-cos(3pi/10),-sin(3pi/10)-.03,A),locate(cos(3pi/10),-sin(3pi/10)-.03,E))}}}