1 Tìm x a) 25x ² – 9=0 b) (x-3) ² – 4=0 c) x ² – 2x =24 d) (x+4) ² – (x+1) (x-1) = 16 e) 3(x-1) ² – 3x(x-

Đáp án:

`a)`\(\left[ \begin{array}{l}x=3/5\\x=-3/5\end{array} \right.\) 

`b)`\(\left[ \begin{array}{l}x=5\\x=1\end{array} \right.\) 

`c)`\(\left[ \begin{array}{l}x=-4\\x=6\end{array} \right.\) 

`d)x=-1/8`

`e)x=-255/2`

Giải thích các bước giải:

`a) 25x ² – 9=0`

`⇒(5x)²-3²=0`

`⇒(5x-3)(5x+3)=0`

`⇒`\(\left[ \begin{array}{l}5x-3=0\\5x+3=0\end{array} \right.\) 

`⇒`\(\left[ \begin{array}{l}5x=3\\5x=-3\end{array} \right.\) 

`⇒`\(\left[ \begin{array}{l}x=3/5\\x=-3/5\end{array} \right.\) 

`b) (x-3) ² – 4=0`

`⇒(x-3)²-2²=0`

`⇒(x-3-2)(x-3+2)=0`

`⇒(x-5)(x-1)=0`

`⇒`\(\left[ \begin{array}{l}x=5\\x=1\end{array} \right.\) 

`c)x²-2x=24`

`⇒ x²-2x-24=0`

`⇒(x+4)(x-6)=0`

`⇒`\(\left[ \begin{array}{l}x=-4\\x=6\end{array} \right.\) 

`d)(x+4)²-(x+1)(x-1)=16`

`⇒x²+8x+16-x²+1-16=0`

`⇒8x=-1`

`⇒x=-1/8`

`e)(2x-1)²+(x+3)²-5(x+7)(x-7)=0`

`⇒4x²-4x+1+x²+6x+9-5x²+245=0`

`⇒2x+255=0`

`⇒x=-255/2`

Bạn tham khảo ạ !