Question

Làm bài 21 phần e và f

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

\(x^2-x-\left(3x-3\right)=0\)

Answer 1

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

\(\Leftrightarrow4x^2-20x+25-\left(x^2+4x+4\right)=0\)

\(\Leftrightarrow4x^2-20x+25-x^2-4x-4=0\)

\(\Leftrightarrow3x^2-24x+21=0\)

\(\Leftrightarrow3x^2-21x-3x+21=0\)

\(\Leftrightarrow3x\left(x-7\right)-3\left(x-7\right)=0\)

\(\Leftrightarrow\left(x-7\right)\left(3x-3\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=7\\x=1\end{matrix}\right.\)

\(x^2-x-\left(3x-3\right)=0\)

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

\(\Leftrightarrow x\left(x-1\right)-3\left(x-1\right)=0\)

\(\Leftrightarrow\left(x-1\right)\left(x-3\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=1\\x=3\end{matrix}\right.\)