2005 iTest Problems/Problem 52

Problem

If the product of $(\sqrt2 +\sqrt3+\sqrt5) (\sqrt2 +\sqrt3-\sqrt5) (\sqrt2 -\sqrt3+\sqrt5) (-\sqrt2 +\sqrt3+\sqrt5)$ is $12\sqrt6+ 6\sqrt{x}$ , find $x$.

IMPORTANT NOTE: This problem was thrown out of the actual competition.

Solution (credit to Mathzeus1024)

The entire product computes to $24$. Thus:

$\sqrt{x} = \frac{24 - 12\sqrt{6}}{6} = 4 - 2\sqrt{6}$;

or $x = [4 - 2\sqrt{6}]^2 = 40 - 16\sqrt{6}$.

Note: The problem writers intended for it to equal a value where $x$ was an integer. This appears to be why it was thrown out.

See Also

2005 iTest (Problems, Answer Key)
Preceded by:
Problem 51
Followed by:
Problem 53
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 TB1 TB2 TB3 TB4