Algebra · real student question

Solve the inequality 5 minus one half of (x + 4) is greater than or equal to 4.

Question

Solve for xx:

512(x+4)45-\frac12(x+4)\ge 4

Step-by-step solution

  1. Distribute the 12-\frac12 over the bracket. Both terms inside are affected:

    512x245-\frac12x-2\ge 4

    since 124=2-\frac12\cdot 4=-2. Keeping the minus sign attached to the fraction is what makes the next steps come out right.

  2. Combine the constants on the left.

    52=3312x45-2=3\quad\Rightarrow\quad 3-\frac12x\ge 4

  3. Isolate the xx term. Subtract 33 from both sides — an addition, so the direction is untouched:

    12x1-\frac12x\ge 1

  4. Multiply by 2-2 and reverse the inequality. This is the crux: multiplying or dividing by a negative number flips \ge into \le:

    x2x\le -2

    Leaving it as x2x\ge -2 would give exactly the wrong half of the line.

  5. Test three points to be sure. At x=2x=-2: 512(2)=45-\frac12(2)=4, and 444\ge 4 holds (so the endpoint is included). At x=4x=-4: 50=545-0=5\ge 4 ✓. At x=0x=0: 52=35-2=3, and 343\ge 4 is false ✓. So the solution is x2x\le -2, i.e. x(,2]x\in(-\infty,-2].

Answer

x2,x(,2]x\le -2,\qquad x\in(-\infty,-2]

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