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Fie x1,x2 solutiile ecuatiei x²-2*x-4=0.Sa se calculeze 2*(x1+x2)-x1*x2


Răspuns :

x²-2x-4=0
a=1
b=-2
c=-4
Δ=b²-4ac=(-2)²-4·1·(-4)=4+16=20
x1=(-b+√Δ)/2a=(2+√20)/2=(2+2√5)/2=2(1+√5)/2=1+√5
x2=(-b-√Δ)/2a=1-√5
2(x₁+x₂)-x₁x₂=2(1+√5+1-√5)-(1+√5)(1-√5)=2·2-(1-√5+√5-5)=4+4=8