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#1
09 ¡Ñ¹ÂÒ¹ 2012, 20:49
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àŢ¡¡ÓÅѧ
$1. 144^{a+b} = 36 , 15^{3a+2b} = 1 ¨§ËÒ 2(12^{a+2}+12^{b-2}) = ?$
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#2
09 ¡Ñ¹ÂÒ¹ 2012, 21:55
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$15^{3a+2b} = 1 = 15^0 \ \ $
$3a+2b = 0 \ \ \ \to 3a = -2b, \ \ 2b = -3a$ $144^{a+b} = 36$ $[(12)^2]^{a+b} = 12^{2a+2b} = 12^{2a-3a} = 12^{-a} = 6^2 \ \ \to 12^a = 6^{-2}$ ...* $12^{a+b} = 6$ $[12^{a+b}]^3 = 6^3$ $12^{3a+3b} = 12^{-2b+3b} = 12^b = 6^3$....** ·ÓµèÍàͧä´éáÅéǹФÃѺ
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#4
09 ¡Ñ¹ÂÒ¹ 2012, 22:59
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ÍéÒ§ÍÔ§:
µÍº 11 ¤ÃѺ
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