\(A=x^2-6x+10\)

\(\Leftrightarrow A=x^2-2\cdot x\cdot3+3^2-9+10\)

\(\Leftrightarrow A=\left(x-3\right)^2+1\ge1\)     \(\forall x\in z\)

\(\Leftrightarrow A_{min}=1khix=3\)

\(B=3x^2-12x+1\)

\(\Leftrightarrow B=\left(\sqrt{3}x\right)^2-2\cdot\sqrt{3}x\cdot2\sqrt{3}+\left(2\sqrt{3}\right)^2-12+1\)

\(\Leftrightarrow B=\left(\sqrt{3}x-2\sqrt{3}\right)^2-11\ge-11\)    \(\forall x\in z\)

\(\Leftrightarrow B_{min}=-11khix=2\)

Ta có : \(C=\dfrac{5-x^2}{x^2+3}\)

\(=\dfrac{-\left(x^2+3\right)+8}{x^2+3}=\dfrac{8}{x^2+3}-1\)

Ta sẽ có : \(x^2\ge0\Rightarrow x^2+3\ge3\Rightarrow\dfrac{8}{x^2+3}\le\dfrac{8}{3}\)

\(\Rightarrow C=\dfrac{8}{x^2+3}-1\le\dfrac{8}{3}-1=\dfrac{5}{3}\)

Vậy : \(MaxC=\dfrac{5}{3}\Leftrightarrow x=0.\)

Để C lớn nhất thì x² + 3 nhỏ nhất

Ta có:

x² ≥ 0 với mọi x R

⇒ x² + 3 ≥ 3 với mọi x R

⇒ x² + 3 nhỏ nhất là 3 khi x = 0

⇒ max C = (5 - 0²)/(0² + 3) = 5/3

A= 9- 2.(x^2-2x+ 1)= 9- 2.(x-1)²

Lại có (x-1)² \(\ge\)0 => A\(\le\)9 

Vậy max A =9 <=> x-1=0 => x=1

b, B= 139/3-((x.√3)²+2.√3.2/(√3)+4/3)

= 139/3-(√3.x+2/√3)²

Lại có (√3.x+2/√3)²\(\ge\)0 => B\(\le\)139/3

Vậy maxB = 139/3 <=> x = -2/3

c,C= 25-2(x^2-2.x.3+9)= 25- 2(x-3)²

Laạạiại ccó (x-3)²\(\ge\)0

=> C\(\le\)25

Để max C = 25 <=> x-3= 0 <=> x=3

d, D=2163-( x^2-2.x.12+144)= 2163-(x-12)²

Lại có (x-12)²\(\ge\)0 

=> D\(\le\)2163

Để max D = 2163 <=> x-12 = 0 <=> x= 12

hình như bạn nhầm đề à

Nhầm đề câu nào hả cậu ? Tìm gtln mà

a: \(A=\dfrac{x-2-2x-4+x}{\left(x-2\right)\left(x+2\right)}\cdot\dfrac{-\left(x-2\right)\left(x+1\right)}{6\left(x+2\right)}\)

\(=\dfrac{-6}{\left(x+2\right)}\cdot\dfrac{-\left(x+1\right)}{6\left(x+2\right)}=\dfrac{\left(x+1\right)}{\left(x+2\right)^2}\)

b: A>0

=>x+1>0

=>x>-1

c: x^2+3x+2=0

=>(x+1)(x+2)=0

=>x=-2(loại) hoặc x=-1(loại)

Do đó: Khi x^2+3x+2=0 thì A ko có giá trị

B1: ĐXXĐ: \(x\ne\pm2;x\ne-1\)

\(=\left(\dfrac{x-2}{\left(x+2\right)\left(x-2\right)}-\dfrac{2\left(x+2\right)}{\left(x+2\right)\left(x-2\right)}+\dfrac{x}{\left(x+2\right)\left(x-2\right)}\right):\dfrac{-6\left(x+2\right)}{\left(x-2\right)\left(x+1\right)}\)

\(=\left(\dfrac{x-2-2x-2+x}{\left(x+2\right)\left(x-2\right)}\right):\dfrac{-6\left(x+2\right)}{\left(x-2\right)\left(x+1\right)}\)

\(=\dfrac{-4}{\left(x+2\right)\left(x-2\right)}:\dfrac{-6\left(x+2\right)}{\left(x-2\right)\left(x+1\right)}\)

\(=\dfrac{-4}{\left(x+2\right)\left(x-2\right)}.\dfrac{\left(x-2\right)\left(x+1\right)}{-6\left(x+2\right)}=\dfrac{2\left(x+1\right)}{3\left(x+2\right)^2}\)

b, \(A=\dfrac{2\left(x+1\right)}{3\left(x+2\right)^2}>0\)

\(\Leftrightarrow2x+2>0\) (vì \(3\left(x+2\right)^2\ge0\forall x\))

\(\Leftrightarrow x>-1\).

-Vậy \(x\in\left\{x\in Rlx>-1;x\ne2\right\}\) thì \(A>0\).

a) \(x^2+2x+1\)

\(=\left(x+1\right)^2\)

b) \(9-24x+16x^2\)

\(=\left(3-4x\right)^2\)

c) \(4x^2+\dfrac{1}{4}+2x\)

\(=4x^2+2x+\dfrac{1}{4}\)

\(=\left(2x+\dfrac{1}{2}\right)^2\)

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

a, \(\dfrac{x}{x+2}\) + \(\dfrac{2x}{x-2}\) -\(\dfrac{3x^2-4}{x^2-4}\)

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

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

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

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

Có vài bước mình làm tắc á nha :>