Wednesday, October 8, 2008

Problem Of The Week 46

Let be distinct positive reals. Determine the minimum value of \frac{1}{(x-y)^2}+\frac{16}{xy}+6(x+y) and determine when that minimum occurs.

Source: ALtheman's problem column

3 comments:

  1. Now first looking at the terms, the first thing I instinctively did was, I took y=x+1..so now the equation reduces to 1+16/(x*(x+1))+6(2x+1)..The function will be increasing in the interval (0,1) and after 1. So the minimum is obtained at x=1 which is 27

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  2. Oops interchanged x and y..I considered 1/(y-x)^2

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  3. minimum value occurs..when x=2 y=1 or y=2 x=1...
    the expression equals 27...for any other positive value the expression is greater than this....
    Let x=ky
    1/(y^2(k-1)^2)+ 16/(K*y^2)+ 6y(k+1)
    we can try substituing values for K and Y....

    I dont think this is best approach...just trial and error

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