Question

Tìm x

2) 2 (x + 5) - x\(^2\) - 5x = 0

3) x\(^2\) + 3x + 2 = 0

4) x\(^2\) - 4x - 5 = 0

5) -2x\(^2\) - 3x + 5 = 0

Answer 1

2(x+5)-x²-5x=0

<=> 2(x+5)-(x²+5x)=0

<=> 2(x+5)-x(x+5)=0

<=> (x+5)(2-x)=0

<=> \(\left\{{}\begin{matrix}x+5=0\\2-x=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=-5\\x=2\end{matrix}\right.\)

Vậy ...

x²+3x+2=0

<=> x²+x+2x+2=0

<=> (x²+x)+(2x+2)=0

<=> x(x+1)+2(x+1)=0

<=> (x+1)(x+2)=0

<=> \(\left\{{}\begin{matrix}x+1=0\\x+2=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=-1\\x=-2\end{matrix}\right.\)

Vậy ....

x²-4x-5=0

<=> x2-x+5x-5=0

<=>(x2-x)+(5x-5)=0

<=> x(x-1)+5(x-1)=0

<=> (x-1)(x+5)=0

<=> \(\left\{{}\begin{matrix}x-1=0\\x+5=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=1\\x=-5\end{matrix}\right.\)

Vậy .....

Answer 2

1) 2. (x + 5) - x² - 5x = 0

⇒ 2. (x + 5) - x. ( x - 5 ) = 0 ⇒ ( x - 5 ).(2 - x ) = 0

⇒ \(\left[{}\begin{matrix}x-5=0\\2-x=0\end{matrix}\right.\) ⇒ \(\left[{}\begin{matrix}x=5\\x=2\end{matrix}\right.\)

Vậy x = 5 ; x= 2

2) x² + 3x + 2 = 0 ⇒ x² + x + 2x + 2 = 0

⇒ ( x² + x ) + ( 2x + 2 ) = 0

⇒ x. ( x + 1 ) + 2. ( x + 1 ) = 0

⇒ ( x +1 ).(x + 2 ) = 0 ⇒ \(\left[{}\begin{matrix}x+1=0\\x+2=0\end{matrix}\right.\) ⇒ \(\left[{}\begin{matrix}x=-1\\x=-2\end{matrix}\right.\)

Vậy x = -1; x = -2

3) x² - 4x -5 = 0 ⇒ x² + x - 5x - 5 = 0

⇒ ( x² + x ) - ( 5x + 5 ) = 0

⇒ x. ( x + 1 ) - 5. ( x + 1 ) = 0

⇒ ( x + 1 ).( x - 5 ) = 0

⇒ \(\left[{}\begin{matrix}x+1=0\\x-5=0\end{matrix}\right.\) ⇒ \(\left[{}\begin{matrix}x=-1\\x=5\end{matrix}\right.\)

Vậy x = -1 ; x = 5

4) - 2x² - 3x + 5 = 0 ⇒ -2x² + 2x - 5x + 5 = 0

⇒ -2x. ( x - 1 ) - 5. ( x - 1 ) = 0

⇒ ( x - 1 ). ( -2x - 5 ) = 0

⇒ \(\left[{}\begin{matrix}x-1=0\\-2x-5=0\end{matrix}\right.\) ⇒ \(\left[{}\begin{matrix}x=1\\-2x=5\end{matrix}\right.\) ⇒ \(\left[{}\begin{matrix}x=1\\x=-\dfrac{5}{2}\end{matrix}\right.\)

Vậy x = 1 ; x = -\(\dfrac{5}{2}\)

Answer 3

2) 2(x+5) - x² - 5x =0

<=> 2(x+5) -x(x+5)=0

<=> (x+5)(2-x)=0

<=>\(\left[{}\begin{matrix}x-5=0\\2-x=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=5\\x=2\end{matrix}\right.\)

vậy ...

3)x² +3x+2=0

<=> x² + 2x +x +2=0

<=> x(x+2) + (x+2)=0

<=>(x+1)(x+2)=0

<=>\(\left[{}\begin{matrix}x+1=0\\x+2=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-1\\x=-2\end{matrix}\right.\)

vậy...

4) x² - 4x - 5x=0

<=> x² -5x+x - 5=0

<=> x(x-5) + (x-5)=0

<=> (x-5)(x+1)=0

<=>\(\left[{}\begin{matrix}x-5=0\\x+1=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=5\\x=-1\end{matrix}\right.\)

vậy...

5) -2x² -3x + 5=0

<=> -2x² +2x-5x+5=0

<=>-2x(x-1) - 5(x-1)=0

<=> (x-1)(-2x-5)=0

<=>\(\left[{}\begin{matrix}x-1=0\\-2x-5=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=1\\-2x=5\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=1\\x=-\dfrac{5}{2}\end{matrix}\right.\)

vậy...