Question

2x^2-4x-5

Answer 1

sửa : tìm GTNN  của 2x^2-4x-5

đặt 

A=\(2x^2-4x-5=2x^2-4x-2-3=2\left(x^2-2x-1\right)-3\)

\(=2\left(x-1\right)^2-3\)

Vì \(2\left(x-1\right)^2\ge0\forall x\)

\(=>2\left(x-1\right)^2-3\ge-3\)

''='' khi \(\left(x-1\right)^2=0\Leftrightarrow x-1=0\Leftrightarrow x=1\)

vậy \(Min_A=-3\left(khi:x=1\right)\)

 

Answer 2

`2x^2 -4x-5`

`=2x^2 -4x+2-7`

`=2(x^2 -2x+1)-7`

`=2(x-1)^2 -7`

`=(\sqrt{2}x-\sqrt{2})^2 -7`

`=(\sqrt{2}x-\sqrt{2}-\sqrt{7})(\sqrt{2}x-\sqrt{2}+\sqrt{7})`

Answer 3

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