Giải thích các bước giải:
\(\begin{array}{l}
a)f\left( x \right) = \left( {x + 1} \right)\left( {x - 1} \right)\left( {3x - 6} \right)\\
f\left( x \right) = 0\\
\to \left( {x + 1} \right)\left( {x - 1} \right)\left( {3x - 6} \right) = 0\\
\to \left[ \begin{array}{l}
x = - 1\\
x = 1\\
x = 2
\end{array} \right.
\end{array}\)
BXD:
x -∞ -1 1 2 +∞
f(x) - 0 + 0 - 0 +
\(\begin{array}{l}
b)f\left( x \right) = \left( {2x - 7} \right)\left( {4 - 5x} \right)\\
f\left( x \right) = 0\\
\to \left( {2x - 7} \right)\left( {4 - 5x} \right) = 0\\
\to \left[ \begin{array}{l}
x = \dfrac{7}{2}\\
x = \dfrac{4}{5}
\end{array} \right.
\end{array}\)
BXD:
x -∞ 4/5 7/2 +∞
f(x) - 0 + 0 -
\(\begin{array}{l}
c)f\left( x \right) = 3x\left( {2x + 7} \right)\left( {9 - 3x} \right)\\
f\left( x \right) = 0\\
\to 3x\left( {2x + 7} \right)\left( {9 - 3x} \right) = 0\\
\to \left[ \begin{array}{l}
x = 0\\
x = - \dfrac{7}{2}\\
x = 3
\end{array} \right.
\end{array}\)
x -∞ -7/2 0 3 +∞
f(x) + 0 - 0 + 0 -
( câu d bạn xem lại đề nhé )
