Toán Lớp 8: giải phương trình x^3 + 8 = x^2 – 4
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Toán Lớp 8: giải phương trình x^3 + 8 = x^2 – 4
Comments ( 1 )
x^3+8=x^2-4
<=>x^3 -x^2 +12=0
<=> x^3+2x^2-3x^2 – 6x +6x+12=0
<=>x^2(x+2)-3x(x+2)+6(x+2)=0
<=>(x+2)(x^2-3x+6)=0
Do x^2-3x+6=(x-3/2)^2 +15/4>= 15/4 > 0
<=>x+2=0
<=>x=-2
Vậy S={-2}