Min max max

Algebra Level 4

max ( 5 max ( 3 , x ) , 3 + x ) \large \max (5 - \max (3, x), 3 + x)

Let x x be an integer . Find the minimum value of the expression above.

3 2 5 4 1

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1 solution

Chew-Seong Cheong
Jul 10, 2016

When x 3 5 max ( 3 , x ) = 5 x < 3 + x max ( 5 max ( 3 , x ) , 3 + x ) = 3 + x 6 x \ge 3\implies 5-\max(3,x) = 5-x < 3+x \implies \max(5-\max(3,x), 3+x) = 3+x \ge 6 .

When x 3 max ( 3 , x ) = 3 x \le 3\implies \max(3,x) = 3 and 5 max ( 3 , x ) = 5 3 = 2 5-\max(3,x) = 5-3=2 .

When x 1 3 + x 2 x \le -1\implies 3+x \le 2 and max ( 5 max ( 3 , x ) , 3 + x ) = max ( 2 , 2 ) = 2 \max(5-\max(3,x), 3+x) = \max(2, \le 2)=2 .

max ( 5 max ( 3 , x ) , 3 + x ) = { 2 for x 1 3 + x > 2 for x > 1 \implies \max(5-\max(3,x), 3+x) = \begin{cases} 2 & \text{for } x \le -1 \\ 3+x > 2 & \text{for } x > -1 \end{cases}

Therefore, the minimum value of max ( 5 max ( 3 , x ) , 3 + x ) \max(5-\max(3,x), 3+x) is 2 \boxed{2} .

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