[toán 9] câu hỏi ngắn về căn bậc hai

A

angleofdarkness

$\sqrt{13}>\sqrt{12,25}=3,5$

$\sqrt{21}>\sqrt{20,25}=4,5$

$\sqrt{31}>\sqrt{30,25}=5,5$

$\sqrt{43}>\sqrt{42,25}=6,5$

$\sqrt{57}>\sqrt{56,25}=7,5$

$\sqrt{73}>\sqrt{72,25}=8,5$

\Rightarrow $\sqrt{13}+\sqrt{21}+\sqrt{31}+\sqrt{43}+\sqrt{57}+\sqrt{73}>3,5+4,5+5,5+6,5+7,5+8,5 = 36$

\Rightarrow đpcm.
 
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