\(A=\left(x-1\right)^2+8\ge8\\ A_{min}=8\Leftrightarrow x=1\\ B=\left(x+3\right)^2-12\ge-12\\ B_{min}=-12\Leftrightarrow x=-3\\ C=x^2-4x+3+9=\left(x-2\right)^2+8\ge8\\ C_{min}=8\Leftrightarrow x=2\\ E=-\left(x+2\right)^2+11\le11\\ E_{max}=11\Leftrightarrow x=-2\\ F=9-4x^2\le9\\ F_{max}=9\Leftrightarrow x=0\)

(x+2)(4x^2 -2x+1)+(3-2x)(9+6x+4x^2) =  -4x^3+6x^2-3x+29

nha bạn chúc bạn học tốt nha 

Trả lời:

( x + 2 )( 4x² - 2x + 1 ) + ( 3 - 2x )( 9 + 6x + 4x² )

= 4x³ - 2x² + x + 8x² - 4x + 2 + 27 + 18x + 12x² - 18x - 12x² - 8x³ 

= - 4x³ + 6x² - 3x + 29

A=2x⁴-4x³+6x²-4x=2x⁴-4x³+2x²+4x²-4x

=2(x⁴-2x³+x²)+4(x²-x)=2(x²-x)²+4(x²-x)

Mà x²-x=7

=>A=2 .7²+4 .7

Ta có: A=2x\(^4 \)-4x\(^3 \)+6x\(^2 \)-4x

A=2x(x\(^3 \)-2x\(^2\)+3x-2)

A=2x(x\(^3 \)-x\(^2\)-x\(^2\)+x+2x-2)

A=2x(x\(^2\)(x-1)-x(x-1)+2(x-1))

A=2x(x-1)(x² -x+2)

A=2(x²-x)(x²-x+2)

Thay x²-x =7,ta có:

A=2.7.(7+2)=126

a) \(\dfrac{9x^2-6x+1}{9x^2-1}\)

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

\(=\dfrac{3x-1}{3x+1}\)

\(=\dfrac{3\cdot\left(-3\right)-1}{3\cdot\left(-3\right)+1}=\dfrac{-9-1}{-9+1}=\dfrac{-10}{-8}=\dfrac{5}{4}\)

b) Ta có: \(\dfrac{x^2-6x+9}{3x^2-9x}\)

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

\(=\dfrac{x-3}{3x}\)

\(=\dfrac{-\dfrac{1}{3}-3}{3\cdot\dfrac{-1}{3}}=\dfrac{-\dfrac{10}{3}}{-1}=\dfrac{10}{3}\)

c) Ta có: \(\dfrac{x^2-4x+4}{2x^2-4x}\)

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

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

\(=\dfrac{\dfrac{-1}{2}-2}{2\cdot\dfrac{-1}{2}}=\dfrac{-\dfrac{5}{2}}{-1}=\dfrac{5}{2}\)

nhanh giùm mình được không

Bài 1: 

a) Ta có: \(P=1+\dfrac{3}{x^2+5x+6}:\left(\dfrac{8x^2}{4x^3-8x^2}-\dfrac{3x}{3x^2-12}-\dfrac{1}{x+2}\right)\)

\(=1+\dfrac{3}{\left(x+2\right)\left(x+3\right)}:\left(\dfrac{8x^2}{4x^2\left(x-2\right)}-\dfrac{3x}{3\left(x-2\right)\left(x+2\right)}-\dfrac{1}{x+2}\right)\)

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

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

\(=1+\dfrac{3}{\left(x+2\right)\left(x+3\right)}\cdot\dfrac{\left(x-2\right)\left(x+2\right)}{4x+8-x-x+2}\)

\(=1+3\cdot\dfrac{\left(x-2\right)}{\left(x+3\right)\left(2x+10\right)}\)

\(=1+\dfrac{3\left(x-2\right)}{\left(x+3\right)\left(2x+10\right)}\)

\(=\dfrac{\left(x+3\right)\left(2x+10\right)+3\left(x-2\right)}{\left(x+3\right)\left(2x+10\right)}\)

\(=\dfrac{2x^2+10x+6x+30+3x-6}{\left(x+3\right)\left(2x+10\right)}\)

\(=\dfrac{2x^2+19x-6}{\left(x+3\right)\left(2x+10\right)}\)

\(A=6x\left(2x-7\right)-\left(3x-5\right)\left(4x+7\right)\)

\(=12x^2-42x-\left(12x^2+x-35\right)\)

\(=12x^2-42x-12x^2-x+35\)

\(=-43x+35\)

Thay x = -2 vào biểu thức A ta có :

\(A=-43.\left(-2\right)-35=86+35=121\)

Vậy tại x = -2 thì A = 121