1.

\(f\left(x\right)=\frac{x-7}{\left(x-4\right)\left(4x-3\right)}\)

Vậy:

\(f\left(x\right)\) ko xác định tại \(x=\left\{\frac{3}{4};4\right\}\)

\(f\left(x\right)=0\Rightarrow x=7\)

\(f\left(x\right)>0\Rightarrow\left[{}\begin{matrix}\frac{3}{4}< x< 4\\x>7\end{matrix}\right.\)

\(f\left(x\right)< 0\Rightarrow\left[{}\begin{matrix}x< \frac{3}{4}\\4< x< 7\end{matrix}\right.\)

2.

\(f\left(x\right)=\frac{11x+3}{-\left(x-\frac{5}{2}\right)^2-\frac{3}{4}}\)

Vậy:

\(f\left(x\right)=0\Rightarrow x=-\frac{3}{11}\)

\(f\left(x\right)>0\Rightarrow x< -\frac{3}{11}\)

\(f\left(x\right)< 0\Rightarrow x>-\frac{3}{11}\)

3.

\(f\left(x\right)=\frac{3x-2}{\left(x-1\right)\left(x^2-2x-2\right)}\)

Vậy:

\(f\left(x\right)\) ko xác định khi \(x=\left\{1;1\pm\sqrt{3}\right\}\)

\(f\left(x\right)=0\Rightarrow x=\frac{2}{3}\)

\(f\left(x\right)>0\Rightarrow\left[{}\begin{matrix}x< 1-\sqrt{3}\\\frac{2}{3}< x< 1\\x>1+\sqrt{3}\end{matrix}\right.\)

\(f\left(x\right)< 0\Rightarrow\left[{}\begin{matrix}1-\sqrt{3}< x< \frac{2}{3}\\1< x< 1+\sqrt{3}\end{matrix}\right.\)

4.

\(f\left(x\right)=\frac{\left(x-2\right)\left(x+6\right)}{\sqrt{6}\left(x+\frac{\sqrt{6}}{4}\right)^2+\frac{8\sqrt{2}-3\sqrt{6}}{8}}\)

Vậy:

\(f\left(x\right)=0\Rightarrow x=\left\{-6;2\right\}\)

\(f\left(x\right)>0\Rightarrow\left[{}\begin{matrix}x< -6\\x>2\end{matrix}\right.\)

\(f\left(x\right)< 0\Rightarrow-6< x< 2\)

5.

\(f\left(x\right)=\frac{x^2-3x-2}{-\left(x-\frac{1}{2}\right)^2-\frac{3}{4}}\)

Vậy:

\(f\left(x\right)=0\Rightarrow x=\frac{3\pm\sqrt{17}}{2}\)

\(f\left(x\right)>0\Rightarrow\frac{3-\sqrt{17}}{2}< x< \frac{3+\sqrt{17}}{2}\)

\(f\left(x\right)< 0\Rightarrow\left[{}\begin{matrix}x< \frac{3-\sqrt{17}}{2}\\x>\frac{3+\sqrt{17}}{2}\end{matrix}\right.\)

6.

\(f\left(x\right)=\frac{\left(x-1\right)\left(x^2+x-4\right)}{\left(x-1\right)^2\left(x^2-2x-5\right)}=\frac{x^2+x-4}{\left(x-1\right)\left(x^2-2x-5\right)}\)

Vậy:

\(f\left(x\right)\) ko xác định khi \(x=\left\{1;1\pm\sqrt{6}\right\}\)

\(f\left(x\right)=0\Rightarrow x=\left\{\frac{-1\pm\sqrt{17}}{2}\right\}\)

\(f\left(x\right)>0\Rightarrow\left[{}\begin{matrix}\frac{-1-\sqrt{17}}{2}< x< 1-\sqrt{6}\\1< x< \frac{-1+\sqrt{17}}{2}\\x>1+\sqrt{6}\end{matrix}\right.\)

\(f\left(x\right)< 0\Rightarrow\left[{}\begin{matrix}x< \frac{-1-\sqrt{17}}{2}\\1-\sqrt{6}< x< 1\\\frac{-1+\sqrt{17}}{2}< x< 1+\sqrt{6}\end{matrix}\right.\)

giúp mình với mình đang cần gấp

a)\(F\left(x\right)>0\) khi x thuộc \(\left(\frac{-9}{8};\frac{-1}{3}\right)\cup\left(2;-\infty\right)\)

b) ta có công thức ax²+bx+c=0 thì có a(x-x1)(x-x2)

với x là nghiệm của phương trình trên

vây f(x)>0 khi x thuộc\(\left(-\infty;\frac{-1}{2}\right)\cup\left(\frac{1}{2};+\infty\right)\)

c)f(x)>0 khi x thuộc \(\left(-2;\frac{-1}{2}\right)\cup\left(1:+\infty\right)\)

a) f (x) = \(\frac{-4}{3x+1}-\frac{3}{2-x}\)

= \(\frac{-4\left(2-x\right)-3\left(3x+1\right)}{\left(3x+1\right)\left(2-x\right)}=\frac{-8+4-9x-3}{\left(3x+1\right)\left(2-x\right)}\) = \(\frac{-5x-11}{\left(3x+1\right)\left(2-x\right)}\)
BXD : x \(\frac{-11}{5}\) \(\frac{-1}{3}\) 2
f(x) - 0 + \(||\) - \(||\) +

Vậy f(x) < 0 <=> x ∈ ( -∞ ; \(\frac{-11}{5}\) ) U (\(\frac{-1}{3}\) ; 2)
f(x) > 0 <=> x ∈ ( \(\frac{-11}{5}\); \(\frac{-1}{3}\) ) U (2 ; +∞)

b) f(x) = 4x² -1
f(x) = (2x-1)(2x+1)
2x-1 =0 <=> x = \(\frac{1}{2}\)
2x +1 =0 <=> x= \(\frac{-1}{2}\)

BXD : x \(\frac{-1}{2}\) \(\frac{1}{2}\)
f(x) + 0 - 0 +

f(x) >0 khi x ∈ ( -∞ ; \(\frac{-1}{2}\)) U ( \(\frac{1}{2}\); +∞)
f(x) <0 khi x ∈ ( \(\frac{-1}{2}\); \(\frac{1}{2}\))

c) f(x) = \(\frac{2x+1}{\left(x-1\right)\left(x+2\right)}\)
2x +1 = 0 <=> x= \(\frac{-1}{2}\)
x-1 =0 <=> x = 1
x+2 =0 <=> x = -2

BXD : x -2 \(\frac{-1}{2}\) 1
f(x) + \(||\) - 0 + \(||\) -

Vậy f(x) >0 khi x ∈ ( -∞ ;-2) U ( \(\frac{-1}{2}\) ; 1)
f(x)<0 khi x ∈ ( -2 ; \(\frac{-1}{2}\)) U ( 1; +∞)

a/ ĐKXĐ: \(x\ne\left\{1;3\right\}\)

\(\Leftrightarrow\frac{x+5}{x-1}=\frac{x+1}{x-3}-\frac{8}{\left(x-1\right)\left(x-3\right)}\)

\(\Leftrightarrow\left(x+5\right)\left(x-3\right)=\left(x+1\right)\left(x-1\right)-8\)

\(\Leftrightarrow x^2+2x-15=x^2-9\)

\(\Leftrightarrow2x=6\Rightarrow x=3\) (ktm)

Vậy pt vô nghiệm

b/ ĐKXĐ: \(x\ne1\)

\(\Leftrightarrow\frac{x+1}{\left(x-1\right)\left(x+1\right)}+\frac{2}{x^2+x+1}=\frac{3x^2}{\left(x-1\right)\left(x^2+x+1\right)}\)

\(\Leftrightarrow x^2+x+1+2\left(x-1\right)=3x^2\)

\(\Leftrightarrow2x^2-3x+1=0\Rightarrow\left[{}\begin{matrix}x=1\left(ktm\right)\\x=\frac{1}{2}\end{matrix}\right.\)

c/ ĐKXĐ: \(x\ne\pm4\)

\(\Leftrightarrow\frac{5\left(x^2-16\right)}{\left(x-4\right)\left(x+4\right)}+\frac{96}{\left(x-4\right)\left(x+4\right)}=\frac{2x-1}{x+4}+\frac{3x-1}{x-4}\)

\(\Leftrightarrow5x^2-80+96=\left(2x-1\right)\left(x-4\right)+\left(3x-1\right)\left(x+4\right)\)

\(\Leftrightarrow5x^2+16=5x^2+2x\)

\(\Rightarrow x=8\)