\(x^2-11x-26=0\)
\(x^2-13x+2x-26=0\)
\(x.\left(x-13\right)+2.\left(x-13\right)=0\)
\(\left(x+2\right).\left(x-13\right)=0\)
\(\Rightarrow\orbr{\begin{cases}x+2=0\\x-13=0\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}x=-2\\x=13\end{cases}}\)
vậy...
P/S: lớp 7 sai sót mong thông cảm
\(2x^2+7x-4=0\)
\(2x^2+8x-x-4=0\)
\(2x.\left(x+4\right)-\left(x+4\right)=0\)
\(\left(2x-1\right).\left(x+4\right)=0\)
\(\Rightarrow\orbr{\begin{cases}2x=1\\x=-4\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}x=\frac{1}{2}\\x=-4\end{cases}}\)
vậy ...
\(\left(x-2\right).\left(x-3+1\right)=1\)
\(\left(x-2\right)^2=1\)
\(\Rightarrow\orbr{\begin{cases}x=1\\x=3\end{cases}}\)
vậy ...
a) \(x^2-11x-26=0\Leftrightarrow x^2-13x+2x-26=0\)
\(\Leftrightarrow x\left(x-13\right)+2\left(x-13\right)=0\)
\(\Leftrightarrow\left(x+2\right)\left(x-13\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}x+2=0\\x-13=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=-2\\x=13\end{cases}}}\)
b) \(2x^2+7x-4=0\)
\(\Leftrightarrow2x^2-x+8x-4=0\)
\(\Leftrightarrow x\left(2x-1\right)+4\left(2x-1\right)=0\)
\(\Leftrightarrow\left(x+4\right)\left(2x-1\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}x+4=0\\2x-1=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=-4\\x=\frac{1}{2}\end{cases}}}\)
c) (x-2)(x-3)+x-3=0 <=> (x-3)(x-2+1)=0
\(\Leftrightarrow\left(x-3\right)\left(x-1\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}x=3\\x=1\end{cases}}\)
