Đáp án:
`↓↓↓`
Giải thích các bước giải:
`a) (3x+4)^2 - (3x-1)(3x+1)=49`
`⇒9x^2+24x+16-9x²+1=49`
`⇒24x+17=49`
`⇒24x=32`
`⇒x=4/3`
Vậy `x=4/3`
`b) x^2 - 4x + 4=9(x-2)`
`⇒(x-2)²-9(x-2)=0`
`⇒(x-2)(x-2-9)=0`
`⇒(x-2)(x-11)=0`
`⇒`\(\left[ \begin{array}{l}x-2=0\\x-21=0\end{array} \right.\)
`⇒`\(\left[ \begin{array}{l}x=2\\x=11\end{array} \right.\)
Vậy \(\left[ \begin{array}{l}x=2\\x=11\end{array} \right.\)
`c) x^2 - 25= 3x-15`
`⇒x²-5²-3(x-5)=0`
`⇒(x-5)(x+5)-3(x-5)=0`
`⇒(x-5)(x+2)=0`
`⇒`\(\left[ \begin{array}{l}x-5=0\\x+2=0\end{array} \right.\)
`⇒`\(\left[ \begin{array}{l}x=5\\x=-2\end{array} \right.\)
Vậy \(\left[ \begin{array}{l}x=5\\x=-2\end{array} \right.\)
`d) (x+1)^3 + 3(x+1)^2=(x^2 - 2x+4)(x+2)`
`⇒(x+1)^2(x+4)=x³+8`
`⇒(x²+2x+1)(x+4)-x³-8=0`
`⇒x³+2x²+x+4x²+8x+4-x³-8=0`
`⇒6x²+9x-4=0`
`⇒`Sai đề
