Đáp án:
C1:
b) \(x \in \left[ { - 1;\dfrac{3}{2}} \right) \cup \left[ {2; + \infty } \right)\)
Giải thích các bước giải:
\(\begin{array}{l}
C1:\\
a) - 2{x^2} + 7x - 5 > 0\\
\to \left( {5 - 2x} \right)\left( {x - 1} \right) > 0
\end{array}\)
BXD:
x -∞ 1 5/2 +∞
f(x) - 0 + 0 -
\(KL:x \in \left( {1;\dfrac{5}{2}} \right)\)
\(b)DK:x \ne \dfrac{3}{2}\)
BXD:
x -∞ -1(kép) 3/2 2 +∞
f(x) + 0 - // + 0 -
\(KL:x \in \left[ { - 1;\dfrac{3}{2}} \right) \cup \left[ {2; + \infty } \right)\)
Câu 2:
\(\begin{array}{l}
Do:x \in \left( {\pi ;\dfrac{{3\pi }}{2}} \right)\\
\to \cos x < 0\\
{\sin ^2}x + {\cos ^2}x = 1\\
\to \dfrac{{16}}{{49}} + {\cos ^2}x = 1\\
\to {\cos ^2}x = \dfrac{{33}}{{49}}\\
\to \cos x = - \dfrac{{\sqrt {33} }}{7}\\
\to \tan x = \dfrac{4}{{\sqrt {33} }}\\
\cot x = \dfrac{{\sqrt {33} }}{4}
\end{array}\)
