GTNN nak !!!

\(B=x^2-4xy+5y^2+10x-22y+28\)

\(=\left(x^2-4xy+4y^2\right)+\left(10x-20y\right)+\left(y^2-2y+1\right)+27\)

\(=\left[\left(x-2y\right)^2+10\left(x-2y\right)+25\right]+\left(y^2-2y+1\right)+2\)

\(=\left(x-2y+5\right)^2+\left(y-1\right)^2+2\ge2\) có GTNN là 2

Dấu "=" xảy ra \(\Leftrightarrow\hept{\begin{cases}x-2y+5=0\\y-1=0\end{cases}\Leftrightarrow\hept{\begin{cases}x=-3\\y=1\end{cases}}}\)

Vậy \(B_{min}=2\) tại \(x=-3;y=1\)

Bài 1:

\(a,\left(x^2-1\right)^3-\left(x^4+x^2+1\right)\left(x^2-1\right)\)

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

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

\(b,\left(x^4-3x^2+9\right)\left(x^2+3\right)-\left(3+x^2\right)^3\)

\(=x^6+27-27-27x^2-9x^4-x^6\)

\(=-9x^2\left(3-x^2\right)\)

Bài 5:

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

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

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

Với mọi giá trị của x ta có:

\(\left(x-1\right)^2\ge0\Rightarrow\left(x-1\right)^2-2\ge-2\)

Vậy Min A = -2

Để A = -2 thì \(x-1=0\Rightarrow x=1\)

b, \(B=4x^2+4x+5\)

\(=\left(4x^2+4x+1\right)+4\)

\(=\left(2x+1\right)^2+4\)

Với mọi giá trị của x ta có:

\(\left(2x+1\right)^2\ge0\Rightarrow\left(2x+1\right)^2+4\ge4\)

Vậy Min B = 4

Để B = 4 thì \(2x+1=0\Rightarrow2x=-1\Rightarrow x=-\dfrac{1}{2}\)

c, \(C=2x-x^2-4\)

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

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

Với mọi giá trị của x ta có:

\(\left(x-1\right)^2\ge0\Rightarrow-\left(x-1\right)^2\le0\Rightarrow-\left(x-1\right)^2-3\le-3\)Vậy Max C = -3

để C = -3 thì \(x-1=0\Rightarrow x=1\)

NHANH MINH K

B = 5 - 2z²

Vì 2z² ≥ 0 => B = 5 - 2z² ≤ 5

Dấu "=" xảy ra khi 2z² = 0 => z = 0

Vậy B_max là 5 tại z = 0

C = |x - 3| + |5 - x| ≥ |x - 3 + 5 - x| = 2 

Dấu "=" xảy ra khi (x - 3)(5 - x) ≥ 0 <=> 5 ≥ x ≥ 3

Vậy C_min = 2 tại 5 ≥ x ≥ 3

\(A=-\dfrac{4}{x^2-4x+10}\\ =-\dfrac{4}{\left(x^2-2.x.2+4+6\right)}\\ =-\dfrac{4}{\left(x-2\right)^2+6}\)

\(\left(x-2\right)^2\ge0\\ \Rightarrow\left(x-2\right)^2+6\ge6\\ \Rightarrow\dfrac{4}{\left(x-2\right)^2+6}\le\dfrac{2}{3}\\ \Rightarrow A=-\dfrac{4}{\left(x-2\right)^2+6}\ge-\dfrac{2}{3}\)

Min A=-2/3 khi x=2

\(C=\dfrac{2}{x^2+4x+5}=\dfrac{2}{\left(x+2\right)^2+1}\)

Vì \(\left(x+2\right)^2\ge0\Rightarrow\left(x+2\right)^2+1\ge1\)

\(\Rightarrow C\le2\)

Dấu ''='' xảy ra \(\Leftrightarrow x=-2\)

Vậy Min C = 2 kjhi x = -2

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

\(A_{min}=-1\) khi \(x=-2\)

\(A=\dfrac{4x^2+4-4x^2+4x-1}{x^2+1}=4-\dfrac{\left(2x-1\right)^2}{x^2+1}\le4\)

\(A_{max}=4\) khi \(x=\dfrac{1}{2}\)

cm bn

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

\(A_{min}=-1\) khi \(x=2\)

\(A=\dfrac{4x^2+4-4x^2-4x-1}{x^2+1}=4-\dfrac{\left(2x+1\right)^2}{x^2+1}\le4\)

\(A_{max}=4\) khi \(x=-\dfrac{1}{2}\)

cm bn