`a. 27(x-1)^4-x+1=0`
`<=> (x-1)[27(x-1)^3-1]=0`
`<=> (x-1)[27(x^3-3x^2+3x-1)-1]=0`
`<=> (x-1)[27x^3-81x^2+81x-27-1]=0`
`<=> (x-1)[27x^3-36x^2-45x^2+60x+21x-28]=0`
`<=> (x-1)[9x^2(3x-4)-15x(3x-4)+7(3x-4)]=0`
`<=> (x-1)(3x-4)(9x^2-15x+7)=0`
`<=>`\(\left[ \begin{array}{l}x=1\\x=\dfrac{4}{3}\end{array} \right.\)
`b. (x-2)^2-4(2-x)^4=0`
`<=> (x-2)^2[1+4(x-2)^2]=0`
`<=>`\(\left[ \begin{array}{l}x-2=0\\x-2=±\dfrac{1}{2}\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=2\\x=\dfrac{5}{2}\\x=\dfrac{3}{2}\end{array} \right.\)
`c. 4(x-3)-(3-x)^3=0`
`<=> (x-3)[4+(x-3)^2]=0`
`<=> x-3=0`(vì `(x-3)^2\ge0`)
`<=> x=3`
