s.
4/ \(Q=-x^2+2x-7=-\left(x^2-2x+1\right)-6=-\left(x-1\right)^2-6\le-6\)
''='' xaỷ ra khi x - 1 = 0 => x = 1
vậy x = 1 thì Q lớn nhất
2/ \(\left(x-5\right)\left(2x+3\right)-2x\left(x-3\right)+x-7\)
\(=2x^2+3x-10x-15-2x^2+6x+x-7=-15-7=-22\)
1)\(Q=-x^2+2x-7\)
\(\Leftrightarrow Q=-x^2+2x-1-6\)
\(\Leftrightarrow Q=-\left(x^2-2x+1\right)-6\)
\(\Leftrightarrow Q=-\left(x-1\right)^2-6\)
Vậy GTLN của \(Q=-6\) khi \(x-1=0\Leftrightarrow x=1\)
2)\(\left(x-5\right)\left(2x+3\right)-2x\left(x-3\right)+x-7\)
\(=\left(2x^2+3x-10x-15\right)-\left(2x^2-6x\right)+x-7\)
\(=2x^2+3x-10x-15-2x^2+6x+x-7\)
\(=-15-7\)
\(=-22\)
