g)g) 2.(x+5)−x2−5x=02.(x+5)-x2-5x=0

⇒2.(x+5)−x.(x+5)=0⇒2.(x+5)-x.(x+5)=0

⇒(2−x).(x+5)=0⇒(2-x).(x+5)=0

⇒[2−x=0x+5=0⇒[2-x=0x+5=0

⇒[x=2x=−5⇒[x=2x=-5

Vậy x∈{2;−5}x∈{2;-5}

h)h) x2+5x−6=0x2+5x-6=0

⇒x2−x+6x−6=0⇒x2-x+6x-6=0

⇒x.(x−1)+6.(x−1)=0⇒x.(x-1)+6.(x-1)=0

⇒(x+6).(x−1)=0⇒(x+6).(x-1)=0

⇒[x+6=0x−1=0⇒[x+6=0x-1=0

⇒[x=−6x=1⇒[x=-6x=1

Vậy x∈{−6;1}x∈{-6;1}

i)i)

(2x+3)2−4.(x+1).(x−1)=49(2x+3)2-4.(x+1).(x-1)=49

⇒4x2+12x+9−4.(x2−1)=49⇒4x2+12x+9-4.(x2-1)=49

⇒4x2+12x+9−4x2+4=49⇒4x2+12x+9-4x2+4=49

⇒(4x2−4x2)+12x=49−9−4⇒(4x2-4x2)+12x=49-9-4

⇒12.x=36⇒12.x=36

⇒x=3⇒x=3

Vậy x=3x=3

j)j) x3+x2+x+1=0x3+x2+x+1=0

⇒x2.(x+1)+1.(x+1)=0⇒x2.(x+1)+1.(x+1)=0

⇒(x2+1).(x+1)=0⇒(x2+1).(x+1)=0

⇒[x2+1=0x+1=0⇒[x2+1=0x+1=0

⇒[x2=−1(vôlí)x=−1⇒[x2=-1(vôlí)x=-1

Vậy x=−1x=-1

k)k) x3−x2=4x2−8x+4x3-x2=4x2-8x+4

⇒x2.(x−1)=4.(x2−2x+1)⇒x2.(x-1)=4.(x2-2x+1)

⇒x2.(x−1)=4.(x−1)2⇒x2.(x-1)=4.(x-1)2

⇒x2.(x−1)−4.(x−1)2=0⇒x2.(x-1)-4.(x-1)2=0

⇒(x−1).[x2−4.(x−1)]=0⇒(x-1).[x2-4.(x-1)]=0

⇒(x−1).(x2−4x+1)=0⇒(x-1).(x2-4x+1)=0

Trường hợp 1:1:

x−1=0x-1=0

⇒x=1⇒x=1

Trường hợp 2:2:

x2−4x+1=0x2-4x+1=0

⇒(x2−4x+4)=3⇒(x2-4x+4)=3

⇒(x−2)2=(±√3)2⇒(x-2)2=(±3)2

⇒[x−2=√3x−2=−√3⇒[x-2=3x-2=-3

⇒[x=√3+2x≡2−√3⇒[x=3+2x≡2-3

Vậy x∈{1;√3+2;2−√3}
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