Toán Lớp 8: BÀI 1: TÌM X
a)(x-3)^3 – (x – 3)(x^2 + 3x +9 )+9(x+1)^2=15
d)x(x-5)(x+5)-(x+2)(x^2 -2x +4)=3
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Toán Lớp 8: BÀI 1: TÌM X
a)(x-3)^3 – (x – 3)(x^2 + 3x +9 )+9(x+1)^2=15
d)x(x-5)(x+5)-(x+2)(x^2 -2x +4)=3
Comments ( 1 )
<=>x^3-9x^2+27x-27-(x^3-3^3)+9(x^2+2x+1)=15
<=>x^3-9x^2+27x-27-x^3+27+9x^2+18x+9=15
<=>(x^3-x^3)+(-9x^2+9x^2)+(27x+18x)-(27-27)=15-9
<=>45x=6
<=>x=2/15
vậy x=2/15
b)x(x-5)(x+5)-(x+2)(x^2-2x+4)=3
<=>x(x^2-25)-(x^3+8)=3
<=>x^3-25x-x^3-8=3
<=>-25x=3+8
<=>-25x=11
<=>x=-11/25
vậy x=-11/25