※ 引述《ddrmatch ()》之銘言：
: (1)若a,b,c>0且a+b+c=3
: 求 3^a + 3^b + 3^c 之MAX
a,b,c >= 0 才會有max.
for any x,y>=0,
we have (3^x-1)(3^y-1)>=0 => 1+3^(x+y)>=3^x+3^y.
thus, 3^a+3^b+3^c <= 1+3^(a+b)+3^c <= 1+1+3^(a+b+c)=29
"=" holds iff any two of a,b,c are zero.
so, max=29.
: (2)f(x)= 2^x + 2^(-x) + x
: g(x)= k{3^x + 3^(-x)} + x
: 交點PQ支長度為8^(1/2)求K值
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