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D( n )
21*n = 0
7*n^2 = 0
21*n = 0
21*n = 0
21*n = 0 // : 21
n = 0
7*n^2 = 0
7*n^2 = 0
7*n^2 = 0 // : 7
n^2 = 0
n = 0
n in (-oo:0) U (0:+oo)
6/(7*n^2)-(4/(21*n)) = 0
(-4/21)*n^-1+6/(7*n^2) = 0
6/7*n^-2-4/21*n^-1 = 0
t_1 = n^-1
6/7*t_1^2-4/21*t_1^1 = 0
6/7*t_1^2-4/21*t_1 = 0
DELTA = (-4/21)^2-(0*6/7*4)
DELTA = 16/441
DELTA > 0
t_1 = ((16/441)^(1/2)+4/21)/(6/7*2) or t_1 = (4/21-(16/441)^(1/2))/(6/7*2)
t_1 = 2/9 or t_1 = 0
t_1 = 0
n^-1+0 = 0
n^-1 = 0
1*n^-1 = 0 // : 1
n^-1 = 0
n należy do O
t_1 = 2/9
n^-1-2/9 = 0
1*n^-1 = 2/9 // : 1
n^-1 = 2/9
-1 < 0
1/(n^1) = 2/9 // * n^1
1 = 2/9*n^1 // : 2/9
9/2 = n^1
n = 9/2
n = 9/2
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