In the figure above, ABCDE is a regular pentagon with side of length 2. What is the xcoordinate of D ? 4 . 9 0 (a) 2.62 (b) 3.62 (c) 3.73 (d) 3.90 (e) 4.90 Correct Answer: B Explanation: The sum of the measures of the interior angles of a regular pentagon is equal to 3 x 180 = 540°. Each interior angle has a measure of 108°. Using supplementary angles, has a measure of 72°. You can use right triangle trigonometry to find the x-coordinate of point D. Since EF = 2 cos 72° 0.62. Since the length of each side of the pentagon is 2, the x-coordinate of point E is 3. Putting the information together tells us that the x-coordinate of point D is 3.62. The correct answer is (B).