1)
2)

1) 2x² - 17x + 26 = 0
D = 17² - 26·2·4 = 289 - 208 = 81 = 9²
x₁ = (17 + 9)/4 = 26/4 = 13/2
x₂ = (17 - 9)/4 = 8/4 = 2
Ответ: x = 2; 6,5. 

2) cos[π(x - 2)/3] = 1/2
π(x - 2)/3 = ±π/3 + 2πn, n ∈ Z
(x - 2)/3 = ±1/3 + 2n, n ∈ Z
x - 2 = ±1 + 6n, n ∈ Z
x =  ±1 + 2 + 6n, n ∈ Z
Ответ: x =  ±1 + 2 + 6n, n ∈ Z.

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