Đáp án + Giải thích các bước giải:
`a)`
`49x^{2}-25=0`
`<=>(7x-5)(7x+5)=0`
`<=>` \(\left[ \begin{array}{l}7x-5=0\\7x+5=0\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x=\dfrac{5}{7}\\x=-\dfrac{5}{7}\end{array} \right.\)
Vậy `S={+-(5)/(7)}`
`b)`
`(4x-1)^{2}-(3x+2)^{2}=0`
`<=>(4x-1+3x+2)(4x-1-3x-2)=0`
`<=>(7x+1)(x-3)=0`
`<=>` \(\left[ \begin{array}{l}7x+1=0\\x-3=0\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}x=-\dfrac{1}{7}\\x=3\end{array} \right.\)
Vậy `S={-(1)/(7);3}`
`c)`
`(3x-2)^{3}-(3x-2)(9x^{2}+6x+4)+27x(2x-5)=0`
`<=>27x^{3}-54x^{2}+36x-8-(27x^{3}-8)+54x^{2}-135x=0`
`<=>27x^{3}-54x^{2}+36x-8-27x^{3}+8+54x^{2}-135x=0`
`<=>-99x=0`
`<=>x=0`
Vậy `S={0}`
