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cos((3*x)/5)*cos((3*x)/20) = 0
cos((3*x)/5) = 0
cos((3*x)/5) = 0 <=> (3*x)/5 = pi*k_1+pi/2 i k_1 należy do I
t_1 = pi*k_1+pi/2
(3*x)/5-t_1 = 0
3/5*x-t_1 = 0 // + t_1
3/5*x = t_1 // : 3/5
x = t_1/3/5
x = 5/3*t_1
x = 5/3*pi*k_1+pi/2 i k_1 należy do I
cos((3*x)/20) = 0
cos((3*x)/20) = 0 <=> (3*x)/20 = pi*k_2+pi/2 i k_2 należy do I
t_2 = pi*k_2+pi/2
(3*x)/20-t_2 = 0
3/20*x-t_2 = 0 // + t_2
3/20*x = t_2 // : 3/20
x = t_2/3/20
x = 20/3*t_2
x = 20/3*pi*k_2+pi/2 i k_2 należy do I
cos((3*x)/5)*cos((3*x)/20) = 0 <=> cos((3*x)/5) = 0 or cos((3*x)/5)*cos((3*x)/20) = 0 <=> cos((3*x)/20) = 0
x in { 5/3*pi*k_1+pi/2, 20/3*pi*k_2+pi/2 }
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