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Bài giải
a, Ta có : \(A=\frac{x^2-2+1995}{x^2}=\frac{x^2}{x^2}-\frac{2+1995}{x^2}=1-\frac{1997}{x^2}\)
\(A\text{ đạt GTNN khi }\frac{1997}{x^2}\text{ đạt GTLN}\)
\(\Rightarrow\text{ }x^2\text{ nhỏ nhất }\left(x\ne0\right)\) Mà \(x^2\ge0\text{ }\Rightarrow\text{ }x^2=1\text{ }\Rightarrow\text{ }x\in\left\{\pm1\right\}\)
\(\Rightarrow\text{ Min A }=1-\frac{1997}{1}=1-1997=-1996\)
Bo may la binh day k di hieu ashdbfgbgygygggydfsghuyfhdguuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu3
=4x2-4x+1+x2+4x+4
=5x2+5>hoặc =5
vậy gtnn la 5
( 2x - 1 ) + ( x + 2 )2
= 4x2 - 4x + 1 + x2 + 4x + 4
= 5x2 + 5 > hoặc = 5
Vậy GTNN la 5