Đáp án:
a) \(\begin{array}{l}
f\left( x \right) > 0 \Leftrightarrow x \in \left( { - \infty ; - 50} \right) \cup \left( { - \dfrac{1}{2}; + \infty } \right)\\
f\left( x \right) < 0 \Leftrightarrow x \in \left( { - 50; - \dfrac{1}{2}} \right)
\end{array}\)
Giải thích các bước giải:
a) BXD:
x -∞ -50 -1/2 +∞
f(x) + 0 - 0 +
\(\begin{array}{l}
KL:f\left( x \right) > 0 \Leftrightarrow x \in \left( { - \infty ; - 50} \right) \cup \left( { - \dfrac{1}{2}; + \infty } \right)\\
f\left( x \right) < 0 \Leftrightarrow x \in \left( { - 50; - \dfrac{1}{2}} \right)
\end{array}\)
b) BXD:
x -∞ -1/3 2 3 +∞
f(x) - 0 + 0 - 0 +
\(\begin{array}{l}
KL:f\left( x \right) > 0 \Leftrightarrow x \in \left( { - \dfrac{1}{3};2} \right) \cup \left( {3; + \infty } \right)\\
f\left( x \right) < 0 \Leftrightarrow x \in \left( { - \infty ; - \dfrac{1}{3}} \right) \cup \left( {2;3} \right)
\end{array}\)
c) BXD:
x -∞ -4 3/2 2 +∞
f(x) + 0 - 0 + 0 -
d) BXD:
x -∞ -2 1/4 5/3 7/2 +∞
f(x) - 0 + 0 - 0 + 0 -
