\(A=x^2-10x-9\\ =\left(x^2-10x+25\right)-34\\ =\left(x-5\right)^2-34>=-34\)
\(Dấu''=''\ xảy\ ra\ khi :\)\(\left(x-5\right)^2=0< =>x=5\)
\(Vậy\ GTNN\ của\ A\ là :-34\ khi\ x=5\)
\(B=x^2+5x-6\\ =x^2+2.x.\dfrac{5}{2}+\left(\dfrac{5}{2}\right)^2-\dfrac{25}{4}-6\\ =\left(x+\dfrac{5}{2}\right)^2-\dfrac{49}{4}>=-\dfrac{49}{4}\)
\(Dấu ''=''\ xảy\ ra\ khi :\)\(\left(x+\dfrac{5}{2}\right)^2=0< =>x=-\dfrac{5}{2}\)
\(Vậy\ GTNN\ của\ B\ là : -49/4\ khi\ x=-5/2\)
\(A=x^2-10x-9\)
\(=x^2-2x.5+25-16=\left(x-5\right)^2-16\le-16\forall x\in R\)
Dấu = xảy ra khi: \(\left(x-5\right)^2=0\Leftrightarrow x=5\)
Vậy GTNN của A = -16 khi x = 5.
\(B=x^2+5x-6\)
\(=x^2-2x.\dfrac{5}{2}+\dfrac{25}{4}-\dfrac{1}{4}=\left(x-\dfrac{5}{2}\right)^2-\dfrac{1}{4}\le-\dfrac{1}{4}\forall x\in R\)
Dấu = xảy ra khi: \(\left(x-\dfrac{5}{2}\right)^2=0\Leftrightarrow x=\dfrac{5}{2}\)
Vậy GTNN của B = -1/4 khi x = 5/2.
