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Algebra Level 2

( x 2 + 10 x + 27 ) ( y 2 6 y + 11 ) \large (x^{2}+10x+27)(y^{2}-6y+11)

If x x and y y are real numbers, find the minimum possible value of the expression above.


The answer is 4.

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1 solution

Isaac Buckley
Jul 13, 2015

( x 2 + 10 x + 27 ) ( y 2 6 y + 11 ) = ( ( x + 5 ) 2 + 2 ) ( ( y 3 ) 2 + 2 ) (x^{2}+10x+27)(y^{2}-6y+11)\\=((x+5)^2+2)((y-3)^2+2)

We can see the minimum from this is 4 4 and occurs when x = 5 x=-5 and y = 3 y=3

The minimum of the whole expression is the product of the minimum of the two quadratics in this case since they're positive for all values of x x and y y .

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