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Cât e X?
XxX+XxX-X-X-X=-1
X=?


Răspuns :

X x X + X x X - X - X - X = -1 <=> X² + X² - 3X = -1 <=>
2X² - 3X + 1 = 0 => X₁ = [3 +√(9-8) ]/4 = (3+1)/4 = 1
                                X₂ = (3-1)/4 = 2/4 = 1/2