Đáp án:
c) \(f\left( x \right) \le 0\forall x\)
Giải thích các bước giải:
a) BXD:
x -∞ 1 +∞
f(x) - 0 +
\(\begin{array}{l}
KL:f\left( x \right) > 0 \Leftrightarrow x \in \left( {1; + \infty } \right)\\
f\left( x \right) < 0 \Leftrightarrow x \in \left( { - \infty ;1} \right)
\end{array}\)
\(\begin{array}{l}
b)Xét:f\left( x \right) = 0\\
\to - {x^2} + 26x - 1040 = 0\\
Do:\Delta ' = - 871 < 0\\
\to - {x^2} + 26x - 1040 < 0\forall x\\
c)Xét:f\left( x \right) = 0\\
\to - 26{x^2} + 156x - 234 = 0\\
\to x = 3
\end{array}\)
BXD:
x -∞ 3 +∞
f(x) - 0 -
\(KL:f\left( x \right) \le 0\forall x\)
\(\begin{array}{l}
d)Xét:f\left( x \right) = 0\\
\to - {x^2} + 27x - 26 = 0\\
\to \left[ \begin{array}{l}
x = 26\\
x = 1
\end{array} \right.
\end{array}\)
BXD:
x -∞ 1 26 +∞
f(x) - 0 + 0 -
