`y10000` 

`a )`

`x² + 5x - 6 = 0`

`<=> x² + 6x - x - 6 = 0`

`<=> x . ( x + 6 ) . ( x + 6 )`

`<=> ( x - 1 ) . ( x + 6 ) = 0`

`<=>`  \(\left[ \begin{array}{l}x - 1 = 0\\x + 6 = 0\end{array} \right.\) 

`<=>`  \(\left[ \begin{array}{l}x = 1\\x = -6 \end{array} \right.\) 

`b )`

`x² - 5x + 6 = 0`

`<=> x² - 2x - 3x + 6 = 0`

`<=> x . ( x - 2 ) - 3 . ( x - 2 ) = 0`

`<=> ( x - 3 ) . ( x - 2 ) = 0`

`<=>`  \(\left[ \begin{array}{l}x - 3 = 0\\x - 2 = 0\end{array} \right.\) 

`<=>`  \(\left[ \begin{array}{l}x = 3\\x = 2\end{array} \right.\) 

`c )`

`x² - 3x - 18 = 0`

`<=> x² - 6x + 3x - 18 = 0`

`<=> x . ( x - 6 ) + 3 . ( x - 6 ) = 0`

`<=> ( x + 3 ) . ( x - 6 ) = 0`

`<=>` \(\left[ \begin{array}{l}x + 3 = 0\\x - 6 = 0\end{array} \right.\) 

`<=>`  \(\left[ \begin{array}{l}x  = -3\\x  = 6\end{array} \right.\) 

`d )`

`x² - 13x + 36 = 0`

`<=> x² - 9x - 4x + 36 = 0`

`<=> x . ( x - 9 ) - 4 . ( x - 9 ) = 0`

`<=> ( x - 4 ) . ( x - 9 ) = 0`

`<=>` \(\left[ \begin{array}{l}x - 4 = 0\\x - 9 = 0\end{array} \right.\) 

`<=>` \(\left[ \begin{array}{l}x=4\\x=9\end{array} \right.\) 

Đáp án:

`a)x∈{1;-6}`

`b)x∈{2;3}`

`c)x∈{6;-3}`

`d)x∈{4;9}`

Giải thích các bước giải:

`a)x²+5x-6=0`

`⇔x²-x+6x-6=0`

`⇔x(x-1)+6(x-1)=0`

`⇔(x-1)(x+6)=0`

`(1)x-1=0⇔x=1`

`(2)x+6=0⇔x=-6`

Vậy `x∈{1;-6}`

`b)x²-5x+6=0`

`⇔x²-2x-3x+6=0`

`⇔x(x-2)-3(x-2)=0`

`⇔(x-2)(x-3)=0`

`(1)x-2=0⇔x=2`

`(2)x-3=0⇔x=3`

Vậy `x∈{2;3}`

`c)x²-3x-18=0`

`⇔x²-6x+3x-18=0`

`⇔x(x-6)+3(x-6)=0`

`⇔(x-6)(x+3)=0`

`(1)x-6=0⇔x=6`

`(2)x+3=0⇔x=-3`

Vậy `x∈{6;-3}`

`d)x²-13x+36=0`

`⇔x²-4x-9x+36=0`

`⇔x(x-4)-9(x-4)=0`

`⇔(x-4)(x-9)=0`

`(1)x-4=0⇔x=4`

`(2)x-9=0⇔x=9`

Vậy `x∈{4;9}`