`a)(x^4-2x^2+1)+(x^3-x)=0`
`<=>(x^2-1)^2+x(x^2-1)=0`
`<=>(x^2-1)(x^2-1+x)=0`
`<=>[(x^2-1=0),(x^2+x-1=0):}`
`<=>[(x^2=1),(x^2+x+1/4=5/4):}`
`<=>[(x^2=1),((x+1/2)^2=5/4):}`
`<=>[(x=1),(x=-1),(x=(sqrt5-1)/2),(x=(-sqrt5-1)/2):}`
`=>S={1;(sqrt5-1)/2;(-sqrt5-1)/2}`
`b)|x^2-7x+10|=2(x-5)`
Vì `|x^2-7x+10|>=0`
`=>2(x-5)>=0=>x-5>=0=>x>=5`
`pt<=>|(x-2)(x-5)|=2(x-5)`
`x>=5=>x-2>0,x-5>=0`
`=>|(x-2)(x-5)|=(x-2)(x-5)`
`pt<=>(x-5)(x-2-2)=0`
`<=>(x-5)(x-4)=0`
`<=>[(x=5),(x=4):}`
`=>S={5;4}`
`c)x^4-4x^2=0`
`<=>x^2(x^2-4)=0`
`<=>x^2(x-2)(x+2)=0`
`<=>[(x=0),(x=2),(x=-2):}`
`=>S={0;2;-2}.`
