Toán Lớp 8: tìm x:
a) 5x.(x-2020)+x-2020=0
b) x^3-3x^2-4x+12=0
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Toán Lớp 8: tìm x:
a) 5x.(x-2020)+x-2020=0
b) x^3-3x^2-4x+12=0
Comments ( 1 )
a)
5x.(x-2020)+x-2020=0
<=>5x.(x-2020)+(x-2020)=0
<=>(5x+1)(x-2020)=0
<=>[(5x+1=0),(x-2020=0):}
<=>[(5x=-1),(x=2020):}
<=>[(x=-1/5),(x=2020):}
Vậy x\in{-1/5;2020}
b)
x^3-3x^2-4x+12=0
<=>(x^3-3x^2)-(4x-12)=0
<=>x^2.(x-3)-4.(x-3)=0
<=>(x^2-4)(x-3)=0
<=>(x-2)(x+2)(x-3)=0
<=>[(x-2=0),(x+2=0),(x-3=0):}
<=>[(x=2),(x=-2),(x=3):}
Vậy x\in{2;-2;3}