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x la a doua + 5x. + 6 = 0 .... Cat este x?

Răspuns :

x²+5x+6=0
x²+3x+2x+6=0
x(+3)+2(x+3)=0
(x+3)(x+2)=0
x+3=0    x=-3
x+2=0    x=-2
x²+5x+6=0
x²>=0
x²+5x=-6=>5x€Z-
x²-5x=-6 |*(-1)
-x²+5x=6
5x=6+x²
5x-x²=6
x(5-x)=6=> x=-3 deoarece 5x€Z-;5€N
x=-2