x² - x - 11 ≥ 1
x² - x - 11 - 1 ≥ 0
x² - x - 12 ≥ 0
a = 1; b = -1; c = -12;
Δ = b² - 4*1*(-12)
Δ = 1² + 48
Δ = 49;
[tex] x_{1,2} [/tex] = (-b ± √Δ) / (2*a);
[tex] x_{1,2} [/tex] = (-(-1) ± 7) / (2*1);
[tex] x_{1,2} [/tex] = (1 ± 7) / 2;
[tex] x_{1} [/tex] = 4;
[tex] x_{2} [/tex] = -3;
x ∈ (∞; -3] ∪ [4; ∞);
sau
x ∈ R - (-3; 4);
