Toán Lớp 8: Tìm x , biết :
a) ( x-1)^2 = 2x-2
b) 2x^3 + 7x^2 + 5x=0
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Toán Lớp 8: Tìm x , biết :
a) ( x-1)^2 = 2x-2
b) 2x^3 + 7x^2 + 5x=0
Comments ( 2 )
<=> x^2-2x+1=2x-2
<=> x^2-2x+1-2x+2=0
<=> x^2-4x+3=0
<=> x^2-3x-x+3=0
<=> x(x-3)-(x-3)=0
<=> (x-3)(x-1)=0
<=> [(x-3=0),(x-1=0):}
<=> [(x=3),(x=1):}
Vậy S={1;3}
b. 2x^3+7x^2+5x=0
<=> x(2x^2+7x+5)=0
<=> x(2x^2+5x+2x+5)=0
<=> x[x(2x+5)+(2x+5)]=0
<=> x(2x+5)(x+1)=0
<=> [(x=0),(2x+5=0),(x+1=0):}
<=> [(x=0),(x=-5/2),(x=-1):}
Vậy S={-5/2;-1;0}