Question

Tìm x, biết:

a, x³-25x=0

b, 4x²-9-x (2x-3)=0

Answer 1

a) \(x^3-25x=0\)

\(\Leftrightarrow x\left(x^2-25\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=0\\x^2-25=0\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=0\\x=\pm5\end{matrix}\right.\)

b) \(4x^2-9-x\left(2x-3\right)=0\)

\(\Leftrightarrow2x^2+3x-9=0\)

\(\Leftrightarrow2x^2-3x+6x-9=0\)

\(\Leftrightarrow x\left(2x-3\right)+3\left(2x-3\right)=0\)

\(\Leftrightarrow\left(2x-3\right)\left(x+3\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}2x-3=0\\x+3=0\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{3}{2}\\x=-3\end{matrix}\right.\)