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(a-1)(a+2)+(a+1)(a-2)=a^2+a-2+a^2-a-2=2a^2-4=2(a^2-2)
104 = 8*13 = 2*4*13, 78 = 6*13
√3*√104 / √78 = √(3*2*4*13) / √(6*13) = √4 = 2
Частный случай, поэтому
Cosx=0 x=П:2+ Пn.