\(C=x^2-10x+7\)

\(C=x^2-10x+25-18\)

\(C=\left(x-5\right)^2-18\ge-18\)

Dấu "=" xảy ra khi:

\(\left(x-5\right)^2=0\Rightarrow x=5\)

\(P=6x-x^2+2017\)

\(P=-x^2+6x+2017\)

\(P=-x^2+6x-9+2026\)

\(P=-\left(x^2-6x+9\right)+2026\)

\(P=-\left(x-3\right)^2+2026\le2026\)

Dấu "=" xảy ra khi:

\(-\left(x-3\right)^2=0\Rightarrow x=3\)

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

\(A=x^2-x+\dfrac{1}{4}-\dfrac{5}{4}\)

\(A=\left(x-\dfrac{1}{2}\right)^2-\dfrac{5}{4}\ge\dfrac{5}{4}\)

Dấu "=" xảy ra khi:

\(\left(x-\dfrac{1}{2}\right)^2=0\Rightarrow x=\dfrac{1}{2}\)

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

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

\(B=-x^2+3x-\dfrac{9}{4}+\dfrac{17}{4}\)

\(B=-\left(x^2-3x+\dfrac{9}{4}\right)+\dfrac{17}{4}\)

\(B=-\left(x-\dfrac{3}{2}\right)^2+\dfrac{17}{4}\le\dfrac{17}{4}\)

Dấu "=" xảy ra khi:

\(-\left(x-\dfrac{3}{2}\right)^2=0\Rightarrow x=\dfrac{3}{2}\)