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D( x )
cos(x) = 0
cos(x) = 0
cos(x) = 0
cos(x) = 0 <=> x = pi*k_1+pi/2 i k_1 należy do I
t_1 = pi*k_1+pi/2
x-t_1 = 0
x-t_1 = 0 // + t_1
x = t_1
x = pi*k_1+pi/2 i k_1 należy do I
x in {( -oo : +oo ) / < pi*k_1+pi/2 : pi*k_1+pi/2 >} i k_1 -> {I}
(2*cos(2*x))/cos(x) = 0
(2*cos(2*x))/cos(x) = 0 // * cos(x)
2*cos(2*x) = 0
cos(2*x) = 0
cos(2*x) = 0 <=> 2*x = pi*k_1+pi/2 i k_1 należy do I
t_1 = pi*k_1+pi/2
2*x-t_1 = 0
2*x-t_1 = 0 // + t_1
2*x = t_1 // : 2
x = t_1/2
x = pi*k_1+pi/2/2 i k_1 należy do I
2*cos(2*x) = 0 <=> 2 = 0 or 2*cos(2*x) = 0 <=> cos(2*x) = 0
x = pi*k_1+pi/2/2
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