tìm x a)3. (x-1)+ 2x-2x2 =0 b) x2 + 8x + 15 =0
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tìm x a)3. (x-1)+ 2x-2x2 =0 b) x2 + 8x + 15 =0
a) \(3\left(x-1\right)+2x-2x^2=0\)
\(\Leftrightarrow3x-3+2x-2x^2=0\)
\(\Leftrightarrow-2x^2+5x-3=0\)
\(\Leftrightarrow-2x^2+2x+3x-3=0\)
\(\Leftrightarrow-2x\left(x-1\right)+3\left(x-1\right)=0\)
\(\Leftrightarrow\left(x-1\right)\left(-2x+3\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x-1=0\\-2x+3=0\end{matrix}\right.\)\(\Rightarrow\left[{}\begin{matrix}x=1\\x=\dfrac{3}{2}\end{matrix}\right.\)
Vậy..
b) \(x^2+8x+15=0\)
\(\Leftrightarrow x^2+3x+5x+15=0\)
\(\Leftrightarrow\left(x+3\right)\left(x+5\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x+3=0\\x+5=0\end{matrix}\right.\)\(\Rightarrow\left[{}\begin{matrix}x=-3\\x=-5\end{matrix}\right.\)
Vậy..
Tìm x :
a) 3(x - 1 ) + 2x - 2x2 = 0
\(\Leftrightarrow3\left(x-1\right)-2x^2+2x=0\)
\(\Leftrightarrow\) 3\(\left(x-1\right)-2x\left(x-1\right)=0\)
\(\Leftrightarrow\) (x - 1 )( 3-2x) = 0
\(\Leftrightarrow\left[{}\begin{matrix}x-1=0\\3-2x=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=1\\-2x=-3\Rightarrow x=\dfrac{3}{2}\end{matrix}\right.\)
Vậy....
b) x2 + 8x + 15 = 0
\(\Leftrightarrow x^2+3x+5x+15=0\)
\(\Leftrightarrow\) (x2 + 3x ) + ( 5x + 15 ) =0
\(\Leftrightarrow x\left(x+3\right)+5\left(x+3\right)=0\)
\(\Leftrightarrow\left(x+3\right)\left(x+5\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x+3=0\\x+5=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-3\\x=-5\end{matrix}\right.\)
Vậy....