Toán Lớp 7: Bài1: Tìm GTNN
a)A=|x|+1/2
b)B=x+2,3|-1
Bài 2:Tìm GTLN
a)A=1,3-|x+3,2|
b )B=-|3-x|+2,5
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Toán Lớp 7: Bài1: Tìm GTNN
a)A=|x|+1/2
b)B=x+2,3|-1
Bài 2:Tìm GTLN
a)A=1,3-|x+3,2|
b )B=-|3-x|+2,5
Comments ( 1 )
Do:\left| a \right| \ge 0\forall a\\
B1)\\
a)\left| x \right| \ge 0\\
\Leftrightarrow \left| x \right| + \dfrac{1}{2} \ge \dfrac{1}{2}\\
\Leftrightarrow A \ge \dfrac{1}{2}\\
\Leftrightarrow GTNN:A = \dfrac{1}{2}\,khi;x = 0\\
b)B = \left| {x + 2,3} \right| – 1\\
Do:\left| {x + 2,3} \right| \ge 0\\
\Leftrightarrow \left| {x + 2,3} \right| – 1 \ge – 1\\
\Leftrightarrow B \ge – 1\\
\Leftrightarrow GTNN:B = – 1\,khi:x = – 2,3\\
B2)\\
a)A = 1,3 – \left| {x + 3,2} \right|\\
Do:\left| {x + 3,2} \right| \ge 0\\
\Leftrightarrow – \left| {x + 3,2} \right| \le 0\\
\Leftrightarrow 1,3 – \left| {x + 3,2} \right| \le 1,3\\
\Leftrightarrow A \le 1,3\\
\Leftrightarrow GTLN:A = 1,3\,khi:x = – 3,2\\
b)\left| {3 – x} \right| \ge 0\\
\Leftrightarrow – \left| {3 – x} \right| \le 0\\
\Leftrightarrow – \left| {3 – x} \right| + 2,5 \le 2,5\\
\Leftrightarrow B \le 2,5\\
\Leftrightarrow GTLN:B = 2,5\,khi:x = 3
\end{array}$