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Baltic Way 1992 · Problem 8

Algebra

Find all integers satisfying the equation 2x⋅(4−x)=2x+42^{x} \cdot(4-x)=2 x+4.

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Topics

Equations and inequalities · Algebraic manipulation

Solutions

Solution

Solution: Since 2x2^{x} must be positive, we have 2x+44−x>0\frac{2x + 4}{4 - x} > 0 yielding −2<x<4-2 < x < 4. Thus it suffices to check the points −1,0,1,2,3-1, 0, 1, 2, 3. The three solutions are x=0,1,2x = 0, 1, 2.

Contest context

Results from Baltic Way 1992

8 teams

Mean score
5.0 / 5
Scores of 4 or 5
8 / 8
Estonia
5 / 5

Score distribution

00
10
20
30
40
58
All team scores
TeamScore
Denmark5 / 5
St. Petersburg5 / 5
Poland5 / 5
Latvia5 / 5
Iceland5 / 5
Lithuania5 / 5
Estonia5 / 5
Sweden5 / 5