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AE575DRTQ ỨAE65U5W

29/10/2017 at 09:08
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1.let p and q be prime number greater than 3 such that p=q+2. find the remainder when p+q is divided

by 12

2.let a,b,c be the lengths of the sides of a triangle such that 2c+b=abc.find the smallest value of the expression s=\(\dfrac{3}{b+c-a}+\dfrac{4}{c+a-b}+\dfrac{5}{a+b-c}\)

 




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  • ...
    tth 30/10/2017 at 19:42

    tth Coordinator

    2 .We can't fine the smallest value of the expression.

  • ...
    Dao Trong Luan Coordinator 29/10/2017 at 10:37

    1.

    Because p and q are prime number > 3

    => q can equal 3k+1 or 3k+2

    But if q = 3k+1 => p = 3k+1 + 2 = 3k+3 divided by 3 -> wrong

    And if q = 3k+2 => p = 3k+2 + 2 = 3k+4 divided by 3 remainder 1   -> right

    So p+q = 3k+2 + 3k+4 = 6k+6 = \(6\left(k+1\right)⋮6\)

    We have 2 cases:

    \(\left[{}\begin{matrix}k=2h+1\\k=2k\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}6\left(k+1\right)=6\cdot\left(2h+2\right)=12h+12⋮12\\6\left(k+1\right)=6\left(2h+1\right)=12h+6\equiv6\left(mod12\right)\end{matrix}\right.\)So p+q divided by 12 remainder 0 or 6


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