Đáp án:
`a) x^2-16-x+4=0`
`<=> (x-4)(x+4)-(x-4)=0`
`<=> (x-4)(x+4-1)=0`
`<=> (x-4)(x+3)=0`
`<=>` \(\left[ \begin{array}{l}x-4=0\\x+3=0\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x=4\\x=-3\end{array} \right.\)
`b) (3x-2)^2-9x^2+4=0`
`<=> (3x-2)^2-(9x^2-4)=0`
`<=> (3x-2)^2-(3x-2)(3x+2)=0`
`<=> (3x-2)(3x-2-3x-2)=0`
`<=> -4(3x-2)=0`
`<=> 3x-2=0`
`<=> x=2/3`
`c) x^2(x^2+5)-x^2-5=0`
`<=> x^2(x^2+5)-(x^2+5)=0`
`<=> (x^2+5)(x^2-1)=0`
`<=> (x^2+5)(x-1)(x+1)=0`
do `x^2>=0=>x^2+5>=5>0` với `∀x`
`=>`\(\left[ \begin{array}{l}x+1=0\\x-1=0\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x=-1\\x=1\end{array} \right.\)
`d) (x+3)(3-x)+(x+5)^2=13`
`<=> 9-x^2+x^2+10x+25-13=0`
`<=>10x+21=0`
`<=>x=-21/10`
