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D( x )
(1-x-1)^-15 = 0
1-x-1 = 0
(1-x-1)^-15 = 0
(1-x-1)^-15 = 0
-1/(x^15) = 0
1-x-1 = 0
1-x-1 = 0
-1*x = 0 // : -1
x = 0
x in (-oo:0) U (0:+oo)
0.77 = x/((1-x-1)^-15) // - x/((1-x-1)^-15)
0.77-(x/((1-x-1)^-15)) = 0
0.77-1*x*(-x)^15 = 0
0.77-1*x*(-x)^15 = 0
x^16+0.77 = 0
x^16+0.77 = 0
1*x^16 = -0.77 // : 1
x^16 = -0.77
x belongs to the empty set
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