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D( n )
n = 0
n = 0
n = 0
n in (-oo:0) U (0:+oo)
(180*(n-2))/n = 360/n // - 360/n
(180*(n-2))/n-(360/n) = 0
(180*(n-2))/n-360*n^-1 = 0
(180*(n-2))/n-360/n = 0
180*(n-2)-360 = 0
180*n-720 = 0
(180*n-720)/n = 0
(180*n-720)/n = 0 // * n
180*n-720 = 0
180*n-720 = 0 // + 720
180*n = 720 // : 180
n = 720/180
n = 4
n = 4
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