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8∈A
1)8∈A∪B bernoe
2)8∈A∩(3,4,5,8) bernoe
3)8∈A-(3,4,5,8) ne bernoe
4)8∈A∩∅ ne bernoe
Cos^2 a + sin^2 a = 1
sin^2 a = 1 - cos^2a
sin^2 a = 1 - 25/169
sin^2 a = 144/169
sin a = 12/13
Надеюсь, все понятно написано.