Algebra · real student question

The system x > m + 2 and -2x - 1 >= 4m + 1 has no solution, and the equation x + m - 2 = 2 - x has a non-negative integer solution. Find the sum of all integers m that satisfy both conditions.

Question

If the system of inequalities in xx

{x>m+22x14m+1\begin{cases}x>m+2\\ -2x-1\ge 4m+1\end{cases}

has no solution, and the linear equation in xx, x+m2=2xx+m-2=2-x, has a non-negative integer solution, find the sum of all integers mm that satisfy both conditions.

Step-by-step solution

  1. Rewrite the second inequality with x isolated. From 2x14m+1-2x-1\ge 4m+1 we get 2x4m+2-2x\ge 4m+2. Dividing by the negative number 2-2 reverses the direction: x2m1x\le -2m-1.

  2. Translate no solution into a condition on m. The system asks for x>m+2x>m+2 and x2m1x\le -2m-1 at the same time. Such an xx fails to exist exactly when the upper bound does not sit strictly above the lower bound, i.e. 2m1m+2-2m-1\le m+2. That gives 33m-3\le 3m, so m1m\ge -1.

  3. Solve the linear equation. x+m2=2xx+m-2=2-x gives 2x=4m2x=4-m, so x=4m2x=\frac{4-m}{2}.

  4. Impose non-negative integer on that root. Non-negativity needs 4m20\frac{4-m}{2}\ge 0, i.e. m4m\le 4. Integrality needs 4m4-m to be even, so mm must be even.

  5. Intersect the three conditions. Combining m1m\ge -1, m4m\le 4 and mm even over the integers leaves m{0,2,4}m\in\{0,2,4\}.

  6. Check each survivor. m=0m=0: system needs x>2x>2 and x1x\le -1 (empty), root x=2x=2. m=2m=2: x>4x>4 and x5x\le -5 (empty), root x=1x=1. m=4m=4: x>6x>6 and x9x\le -9 (empty), root x=0x=0. All three qualify, and 0+2+4=60+2+4=6.

Answer

0+2+4=60+2+4=6

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