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13̂ƂA

1F2/13

2F8/13

3F18/135/13+1

4F32/136/13+2

5F50/1311/13+3

6F72/137/13+5

7F98/137/13+7

8F128/1311/13+9

9F162/136/13+12

10F200/135/13+15

11F242/138/13+18

12F288/132/13+22

2cos(2/13)-2cos(5/13)+2cos(6/13)-2cos(7/13)+2cos(8/13)-2cos(11/13)

4cos(2/13)-4cos(5/13)+4cos(6/13)13-1

2sin(2/13)-2sin(5/13)+2sin(6/13)-2sin(7/13)+2sin(8/13)-2sin(11/13)=0