Toán Cho M = √x +1 / √x +2 Tìm GTNN của M 08/09/2021 By Valentina Cho M = √x +1 / √x +2 Tìm GTNN của M
`M=(sqrtx +1) / ( sqrtx +2` `M=(sqrtx +2-1) / ( sqrtx +2` `M=(sqrtx +2) / ( sqrtx +2)-1/(sqrtx+2` `M=1-1/(sqrtx+2` `text(vì )sqrtx>=0` `=>sqrtx+2>=2` `=>1/(sqrtx+2)<=1/2` `=>-1/(sqrtx+2)>=-1/2` `=>1-1/(sqrtx+2)>=1/2` `=>M_min=1/2text( khi ) x=0` Trả lời
$M=\dfrac{\sqrt{x}+2-1}{\sqrt{x}+2}= 1-\dfrac{1}{\sqrt{x}+2}$ $\sqrt{x}+2\ge 2$ $\Leftrightarrow \dfrac{1}{\sqrt{x}+2}\le \frac{1}{2}$ $\Leftrightarrow \dfrac{-1}{\sqrt{x}+2}\ge -\dfrac{1}{2}$ $\Leftrightarrow M\ge \dfrac{1}{2}$ $minM=\dfrac{1}{2}\Leftrightarrow x=0$ Trả lời
`M=(sqrtx +1) / ( sqrtx +2`
`M=(sqrtx +2-1) / ( sqrtx +2`
`M=(sqrtx +2) / ( sqrtx +2)-1/(sqrtx+2`
`M=1-1/(sqrtx+2`
`text(vì )sqrtx>=0`
`=>sqrtx+2>=2`
`=>1/(sqrtx+2)<=1/2`
`=>-1/(sqrtx+2)>=-1/2`
`=>1-1/(sqrtx+2)>=1/2`
`=>M_min=1/2text( khi ) x=0`
$M=\dfrac{\sqrt{x}+2-1}{\sqrt{x}+2}= 1-\dfrac{1}{\sqrt{x}+2}$
$\sqrt{x}+2\ge 2$
$\Leftrightarrow \dfrac{1}{\sqrt{x}+2}\le \frac{1}{2}$
$\Leftrightarrow \dfrac{-1}{\sqrt{x}+2}\ge -\dfrac{1}{2}$
$\Leftrightarrow M\ge \dfrac{1}{2}$
$minM=\dfrac{1}{2}\Leftrightarrow x=0$