PT Mũ...plz:D

M

myshop92

[TEX] \[{8^x} + 1 = 2\sqrt[3]{{{2^{x + 1}} - 1}}\] [/TEX]
Đặt [TEX] \[\sqrt[3]{{{2^{x + 1}} - 1}} = u\] [/TEX]
[TEX] \[ = > {u^3} = {2.2^x} - 1\] [/TEX]
=>[TEX] \lef{\begin{ {{2^{3x}} +1=2u}\\{{{2.2}^x}-1={u^3}} [/TEX]
cộng 2 ptr ta đc [TEX] \[{2^{3x}} + {2.2^x} = 2u + {u^3} = > u = {2^x} = > {2^{3x}} - {2.2^x} + 1 = 0 < = > ({2^x} - 1)({2^{2x}} + {2^x} - 1) = 0 [/TEX] = > x=0
 
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