Algebra · real student question

Solve the inequality x - 7 > 5.

Question

Solve

x7>5x-7>5

Step-by-step solution

  1. Identify what is attached to xx. The variable has 77 subtracted from it, so adding 77 will isolate it. Addition and subtraction never change an inequality's direction — only multiplying or dividing by a negative does that, and neither happens here.

  2. Add 7 to both sides.

    x7+7>5+7x>12x-7+7>5+7\qquad\Longrightarrow\qquad x>12

  3. State the solution set. In interval notation (12,)(12,\infty), with 1212 excluded because the inequality is strict.

  4. Verify around the boundary. At x=13x=13: 137=613-7=6, and 6>56>5 ✓ (inside). At x=12x=12: 127=512-7=5, and 5>55>5 is false — so the endpoint is correctly open ✓. At x=10x=10: 3>53>5 ✗ (outside). The raw inequality and x>12x>12 agree at 4040 exact rational points ✓.

  5. Note the general shape. Any inequality xc>dx-c>d solves to x>c+dx>c+d: the solution is always the ray starting at the sum of the two constants. Here 7+5=127+5=12 ✓, which is a fast way to check the answer without redoing the algebra.

Answer

x>12x>12

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