\(4,\\ a,=x^3-3x^2+3x-1-x^3+x^2-x+1=-2x^2+2x\\ b,=x^6+27-27-27x^2-9x^4-x^6=-9x^4-27x^2\\ 5,\\ a,A=\left(x+1\right)^2+3\ge3\\ A_{min}=3\Leftrightarrow x=-1\\ b,B=\left(x+2\right)^2-6\ge-6\\ B_{min}=-6\Leftrightarrow x=-2\)
Bài 3:
a) \(\Rightarrow\left(x-5\right)^2=0\)
\(\Rightarrow x-5=0\Rightarrow x=5\)
b) \(\Rightarrow\left(2x-3\right)\left(x+3\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x=\dfrac{3}{2}\\x=-3\end{matrix}\right.\)
c) \(\Rightarrow3x\left(x-2\right)-x\left(x-2\right)=0\)
\(\Rightarrow2x\left(x-2\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x=0\\x=2\end{matrix}\right.\)
d) \(\Rightarrow\left(2x-1\right)^2=\left(5-x\right)^2\)
\(\Rightarrow\left[{}\begin{matrix}2x-1=5-x\\2x-1=x-5\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=2\\x=-4\end{matrix}\right.\)
Bài 4:
a) \(=x^3-3x^2+3x-1-x^3+x^2-x+1=-2x^2+2x\)
b) \(=x^6+27-x^6-27x^2-9x^4-27=-27x^2-9x^4\)
Bài 5:
a) \(A=\left(x^2+2x+1\right)+3=\left(x+1\right)^2+3\ge3\)
\(minA=3\Leftrightarrow x=-1\)
b) \(B=\left(x^2+4x+4\right)-6=\left(x+2\right)^2-6\ge-6\)
\(minB=-6\Leftrightarrow x=-2\)
