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Changing the Subject Calculator

Make x the subject of a formula by undoing what was done to it, in reverse order. Pick the shape that matches your question and put in the numbers, and the result comes back as a rearranged formula rather than a single value, exactly as an exam expects the answer written.

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Answer

Method, Step by Step

    Worked Example

    Make x the subject of y = 2x + 5.

    1. x has been multiplied by 2 and then had 5 added. Undo them in reverse
    2. Subtract 5 from both sides:y − 5 = 2x
    3. Divide both sides by 2:x = (y − 5) ÷ 2

    Answer: x = (y − 5) ÷ 2

    Try These Yourself

    Make x the subject of y = 3x − 4.Show answerHide answer

    Answer: x = (y + 4) ÷ 3

    Add 4, then divide by 3.

    Make x the subject of y = 5x².Show answerHide answer

    Answer: x = ±√(y ÷ 5)

    Divide by 5, then square root.

    Make x the subject of y = 8 ÷ x.Show answerHide answer

    Answer: x = 8 ÷ y

    Multiply both sides by x, then divide by y.