s**********r
发帖数: 8153 | 1 写错了写错了，是xlog2(1+a/x)=b怎么求 a/x>1。 |
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d*z
发帖数: 150 | 2 The result is 3.
We need to find roots for 2^x-x^12=0
That's
x log2 - 12 logx=0
Because
d(xlog2-12logx)=log2-12/x
So that xlog2-12logx increasing while x<0 and first increase then decrease for
x>0.
So that's at most 3 roots for the equation.
2^(-Inf)-(-Inf)^12<0
2^0-0^12>0
So there's one root for x<0.
2^0-0^12>0
2^(2)-2^12 <0
2^(Inf)-Inf^12>0
So there's two roots for x>0
Total there're 3 roots. |
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s**********r
发帖数: 8153 | 3 其中x is unknown, a and b are known. |
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