`a) (x-1)^2 - (2x+5)^2 =0`
`<=> (x-1-2x-5) (x-1+2x+5) =0`
`<=> (-x-6) (3x+4) =0`
`<=>`\(\left[ \begin{array}{l}x=-6\\x=\cfrac{-4}3\end{array} \right.\)
`b) x^2 - (1-x)^2 - (2x-1)^2 =0`
` <=>(x-1+x) (x+1-x) - (2x-1)^2 =0`
` <=>(2x-1) .1 - (2x-1)^2 =0`
` <=>(2x-1)( 1 - 2x+1) =0`
` <=>(2x-1)( 2 - 2x) =0`
`<=>`\(\left[ \begin{array}{l}x=\cfrac12\\x=1\end{array} \right.\)
`c) x^3 +8 = -2x (x+2) `
`<=> (x +2)(x^2-2x+4) +2x (x+2) =0`
`<=> (x +2)(x^2-2x+4 +2x) =0`
`<=>(x+2)(x^2+4)=0`
Vì `x^2+4>0`
`<=>x+2=0`
`<=>x=-2`
`d) 4x^2 + 8x - 5 =0`
`<=>( 4x^2 + 8x +4)-9 =0`
`<=>( 2x +2)^2-9 =0`
`<=>( 2x +2-3)(2x+2+3) =0`
`<=>( 2x -1)(2x+5) =0`
`<=>`\(\left[ \begin{array}{l}x=\cfrac12\\x=\cfrac{-5}{2}\end{array} \right.\)
