How to do this? (Math)

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1

<p><a href="http://img716.imageshack.us/img716/4198/i9vg.png%5B/url%5D"&gt;http://img716.imageshack.us/img716/4198/i9vg.png&lt;/a&gt;&lt;/p>

<p>Answer is D</p>

<p>I got as far as knowing that a pentagon has 540 degrees.</p>

2

<p>Ok, so the 2 keys here in determining the right answer is that this is a regular pentagon, obviously enough, and that the 2 diagonals have the same length. Now, the problem is pretty self-explanatory. In triangle ABC, AB and BC are congruent (regular pentagon) and AC is a diagonal of unknown length. Triangle CDE is exactly the same concept, and ACE has the diagonals as the 2 congruent sides instead of the sides of the pentagon.</p>

3

<p>In a regular pentagon, all 5 sides are equal. As far as this picture shows, the diagonals seem equal distance. If there are 2 equal sides and a different side on a triangle, the triangle is isosceles, in this case with all three.</p>