[Toán 9] Cm:$8^x+8^y+8^z\geq 4^{x+1}+4^{y+1}+4^{z+1}$

B

bat.nap.quan.tai.hon.em.lan.cuoi

[TEX]VT \geq \frac{1}{3}(2^x+2^y+2^z)(4^x+4^y+4^z) \geq 4(4^x+4^y+4^z)=VP[/TEX]

:rolleyes:
 
B

bat.nap.quan.tai.hon.em.lan.cuoi

C2

ta có

[TEX]8^x+8^x+64 \geq 12.4^x[/TEX]

[TEX]8^y+8^y+64 \geq 12.4^y[/TEX]

[TEX]8^z+8^z+64 \geq 12.4^z[/TEX]

[TEX]4^x+4^y+4^z \geq 48[/TEX]

từ các bđt trên thu đc đpcm :)
 
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