\(A=11-10x-x^2\)
\(=-x^2-10x-25+36\)
\(=-\left(x^2+10x+25\right)+36\)
\(=-\left(x+5\right)^2+36\le36\)
Xảy ra khi \(x=-5\)
\(B=-9x^2+12x-15\)
\(=-9x^2+12x-4-11\)
\(=-\left(9x^2-12x+4\right)-11\)
\(=-\left(3x-2\right)^2-11\le-11\)
Xảy ra khi \(x=\dfrac{2}{3}\)
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M = 11 - 10x - x2 = (- x2 - 10x - 25) + 36
= 36 - (x + 5)2 \(\le36\)
Dấu "=" xảy ra khi x = - 5
M = - 9x2 + 12x - 15 = (- 9x2 + 12x - 4) - 11
= - 11 - (3x - 2)2 \(\le-11\)
Dấu "=" xảy ra khi x = \(\dfrac{2}{3}\)
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