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Secondary II • 2yr.

Hello, we started studying algebra recently and I don’t really understand it.

I have to solve this equation :

3x-9 = (7x) / 3

please answer me quickly


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Explanations (1)

  • Explanation from Alloprof

    Explanation from Alloprof

    This Explanation was submitted by a member of the Alloprof team.

    Team Alloprof • 2yr.


    To solve the expression, we have to find the value of x! There are different methods of doing this, but in your example, transposition seems the most appropriate!

    Transposition consists in isolating the variable in one of the members of the equation using the rules for transforming equations.

    The rules for transforming equations are as follows: 

    • Add the same number to both sides of the equation;
    • Subtract the same number from both sides of the equation;
    • Multiply the two sides of the equation by the same number other than zero;
    • Divide the two sides of the equation by the same number other than zero.

    * Psssst! The sides of the equation are the sides of your equality. So in your question, 3x-9 is one side of the equation..

    So, by following these rules, you apply the principle of the scale: all the operations that you apply on one member must be applied to the other member of the equation.

    To isolate your x, it's always easier to simplify terms that don't have an x ​​at the start. Subsequently, you must perform the opposite operation of a term to simplify it.

    For example, in :

    $$2x + 3 = 4$$

    You want to isolate the x and therefore you subtract the 3 by adding -3 in both sides of the equation. Therefore, you’ll have :

    $$ 2x + 3-3 = 4-3 $$

    $$ 2x = 1$$

    Then, because 2x is a multiplication, you’ll have to divide by 2 each side of the equation :

    $$ \frac{2x}{2} = \frac{1}{2}$$

    Which gives x = 1/2 or x = 0.5

    I hope this guides you in your thinking! You can also visit our page where there are explanatory videos and much more! :)

    Hopefully, that helps! Feel free to ask us more questions if you have any!

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