a: ĐKXĐ: x∉{2;-2;3}

\(A=\left(\frac{4x}{x+2}-\frac{x^3-8}{x^3+8}\cdot\frac{4x^2-8x+16}{x^2-4}\right):\frac{16}{x^2-x-6}\)

\(=\left(\frac{4x}{x+2}-\frac{\left(x-2\right)\left(x^2+2x+4\right)}{\left(x+2\right)\left(x^2-2x+4\right)}\cdot\frac{4\left(x^2-2x+4\right)}{\left(x-2\right)\left(x+2\right)}\right):\frac{16}{\left(x-3\right)\left(x+2\right)}\)

\(=\left(\frac{4x}{x+2}-\frac{4\left(x^2+2x+4\right)}{\left(x+2\right)^2}\right)\cdot\frac{\left(x-3\right)\cdot\left(x+2\right)}{16}\)

\(=\frac{4x\left(x+2\right)-4\left(x^2+2x+4\right)}{\left(x+2\right)^2}\cdot\frac{\left(x-3\right)\left(x+2\right)}{16}=\frac{4x^2+8x-4x^2-8x-16}{\left(x+2\right)}\cdot\frac{x-3}{16}\)

\(=\frac{-16\left(x-3\right)}{16\left(x+2\right)}=\frac{-x+3}{x+2}\)

b: A<0

=>\(\frac{-x+3}{x+2}<0\)

=>\(\frac{x-3}{x+2}>0\)

=>x>3 hoặc x<-2

c: A>=5

=>\(\frac{-x+3}{x+2}-5\ge0\)

=>\(\frac{-x+3-5x-10}{x+2}\ge0\)

=>\(\frac{-6x-7}{x+2}\ge0\)

=>\(\frac{6x+7}{x+2}\le0\)

=>-2<x<=-7/6

x^2+2x+2 x^4+x^3+ax^2+4x+6 x^2-x+a x^4+2x^3+2x^2 -x^3+(a-2)x^2+4x+6 -x^3-2x^2-2x ax^2+6x+6 ax^2+2ax+2a (6-2a)x+(6-2a)

Để đa thức \(x^4+x^3+ax^2+4a+6\) chia hết cho \(x^2+2x+2\)thì:

\(\left(6-2a\right)x+\left(6-2a\right)=0\)

\(\Leftrightarrow\hept{\begin{cases}6-2a=0\\6-2a=0\end{cases}}\Leftrightarrow a=3\)

Vậy a = 3 thì đa thức \(x^4+x^3+ax^2+4a+6\) chia hết cho \(x^2+2x+2\)

a: \(M=\left(\dfrac{x}{\left(x-2\right)\left(x+2\right)}-\dfrac{6}{3\left(x-2\right)}+\dfrac{1}{x+2}\right):\left(x-2+\dfrac{10-x^2}{x+2}\right)\)

\(=\left(\dfrac{x}{\left(x-2\right)\left(x+2\right)}-\dfrac{2}{x-2}+\dfrac{1}{x+2}\right):\dfrac{x^2-4+10-x^2}{x+2}\)

\(=\dfrac{x-2x-4+x-2}{\left(x-2\right)\left(x+2\right)}\cdot\dfrac{x+2}{6}\)

\(=\dfrac{-1}{x-2}\)

b: Để M đạt giá trị lớn nhất thì x-2=-1

hay x=1

c: Để M=3x thì \(\dfrac{-1}{x-2}=3x\)

\(\Leftrightarrow3x^2-6x+1=0\)

\(\text{Δ}=\left(-6\right)^2-4\cdot3\cdot1=36-12=24\)

Vì Δ>0 nên phương trình có hai nghiệm phân biệt là:

\(\left\{{}\begin{matrix}x_1=\dfrac{6-2\sqrt{6}}{6}=\dfrac{3-\sqrt{6}}{3}\\x_2=\dfrac{3+\sqrt{6}}{3}\end{matrix}\right.\)

Tử mẫu không rõ rằng

a: ĐKXĐ: x<>2; x<>-2; x<>0; x<>3

b: \(P=\left(\dfrac{-\left(x+2\right)}{x-2}+\dfrac{4x^2}{\left(x-2\right)\left(x+2\right)}+\dfrac{x-2}{x+2}\right)\cdot\dfrac{x^2\left(2-x\right)}{x\left(x-3\right)}\)

\(=\dfrac{-x^2-4x-4+4x^2+x^2-4x+4}{\left(x-2\right)\left(x+2\right)}\cdot\dfrac{-x\left(x-2\right)}{x-3}\)

\(=\dfrac{4x^2-8x}{\left(x+2\right)}\cdot\dfrac{-x}{\left(x-3\right)}=\dfrac{-4x^2\left(x-2\right)}{\left(x+2\right)\left(x-3\right)}\)

c: 2(x-1)=6

=>x-1=3

=>x=4

Thay x=4 vào P, ta đc:

\(P=\dfrac{-4\cdot4^2\cdot\left(4-2\right)}{\left(4+2\right)\left(4-3\right)}=\dfrac{-64\cdot2}{6}=\dfrac{-128}{6}=-\dfrac{64}{3}\)

Thay x=-1 vào phương trình, ta được:

\(2\left\lbrack4\cdot\left(-1\right)+1\right\rbrack+6=\frac{\left(-1+3\right)}{2\cdot\left(-1\right)+k}\)

=>\(\frac{2}{-2+k}=2\cdot\left\lbrack-4+1\right\rbrack+6=0\)

=>k∈∅