Maths Olympiad Prep

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Problem 228

Algebra Difficulty 1.9 Find the answer CEMC Pascal

If xx is a number less than -2, which of the following expressions has the least value: xx, x+2x+2, 12x\frac{1}{2}x, x2x-2, or 2x2x?

A number or a short expression. Fractions can be typed as 3/2, and spacing doesn't matter.

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Official solution

For any negative real number xx, the value of 2x2x will be less than the value of 12x\frac{1}{2}x. Therefore, 12x\frac{1}{2}x cannot be the least of the five values. Thus, the least of the five values is either x2x-2 or 2x2x. When x<2x < -2, we know that 2x(x2)=x+2<02x - (x-2) = x + 2 < 0. Since the difference between 2x2x and x2x-2 is negative, then 2x2x has the smaller value and so is the least of all five values.

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