Inequalities: watch it solved step by step

Solve a linear inequality, flip the sign when dividing by a negative, and test the answer on a number line. Level: GCSE. Type any problem of this kind and the Lab works it out and animates every move, with a plain-words explanation of why.

Worked example: -2x + 1 >= 9

  1. The inequality. Solving an inequality is like solving an equation, but the answer is a range of values, not one number.
  2. Move the number to the right. Subtract 1 on both sides.
  3. Divide by the negative number: FLIP the sign. Dividing by -2, a negative number, reverses the inequality: becomes . This is the step people forget.
  4. Check with test values. Pick a value inside the range and one outside it, and put each into the original inequality. The inside value should make it true, the outside value false.

Answer: x ≤ -4

Practise inequalities with problems the Lab marks for you.

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