$\eqalign{
& \cos i: \cr
& {4^a} + {9^b} + {16^c} = \underbrace {{{{4^a}} \over 4} + {{{4^a}} \over 4} + .. + {{{4^q}} \over 4}}_{4\;so} + \underbrace {{{{9^b}} \over 9} + {{{9^b}} \over 9}}_{9\;so} + \underbrace {{{{{16}^c}} \over {16}} + ... + {{{{16}^c}} \over {16}}}_{16} \ge 29\root {29} \of {{4^{4a - 4}}{9^{9b - 9}}{{16}^{16c - 16}}} \cr
& \to \sqrt {{4^a} + {9^b} + {{16}^c}} \ge \root {58} \of {{{29}^{29}}{4^{4a - 4}}{9^{9b - 9}}{{16}^{16c - 16}}} \cr
& tuong\;tu\;cho\;hai\;cai\;bieu\;thuc\;sau \cr
& \to \sqrt {{4^a} + {9^b} + {{16}^c}} + \sqrt {{9^a} + {{16}^b} + {4^c}} + \sqrt {{{16}^a} + {4^b} + {9^c}} \cr
& \ge \root {58} \of {{{29}^{29}}{4^{4a - 4}}{9^{9b - 9}}{{16}^{16c - 16}}} + \root {58} \of {{{29}^{29}}{4^{4b - 4}}{9^{9c - 9}}{{16}^{16a - 16}}} + \root {58} \of {{{29}^{29}}{4^{4c - 4}}{9^{9a - 9}}{{16}^{16b - 16}}} \cr
& \cos i: \cr
& \root {58} \of {{{29}^{29}}{4^{4a - 4}}{9^{9b - 9}}{{16}^{16c - 16}}} + \root {58} \of {{{29}^{29}}{4^{4b - 4}}{9^{9c - 9}}{{16}^{16a - 16}}} + \root {58} \of {{{29}^{29}}{4^{4c - 4}}{9^{9a - 9}}{{16}^{16b - 16}}} \ge 3\root 3 \of {\root {58} \of {{{29}^{87}}*{4^{4\left( {a + b + c} \right) - 12}}*{9^{9\left( {a + b + c} \right) - 27}}*{{16}^{16\left( {a + b + c} \right) - 48}}} } = 3\sqrt {29} \cr
& dau = \leftrightarrow a = b = c = 1 \cr} $
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