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    I have a small test on C2 maths concerning trigonometry and circles and so forth, and I need to know how to change the subject of an equation to help in the test. I know the basics, but can't figure out this one question:
    'Make x the subject of this equation:
    (x+c)/d = 2(x+e)/f '
    Can anyone help me work it out?
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    (Original post by alexyboi)
    Im not sure if this is correct but this is what i didexpand = (2x 2e)/ftimes the denominator = f(x c) = d(2x 2e)expand again = fx fc = 2dx 2deminus fc fx= 2dx 2de-fcdivide by f x= (2dx 2de-fc)/fI don't do maths but i do chem and bio AS sorry if its wrongGood luck x
    Thanks for trying to help - I've got the answer in a booklet but it's different to yours (I had just needed to understand how to work it out) but you definitely gave it a good go for not doing AS maths Thank you anyway!
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    (Original post by studentdying999)
    Thanks for trying to help - I've got the answer in a booklet but it's different to yours (I had just needed to understand how to work it out) but you definitely gave it a good go for not doing AS maths Thank you anyway!
    Have you tried working it out? Where did you get stuck?
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    (Original post by Sonechka)
    Have you tried working it out? Where did you get stuck?
    I have but I'm not sure whether to expand the brackets on the right hand side, or what values I should move to what side etc. I'm just confused about how to do this question as a whole :/
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    (Original post by studentdying999)
    I have but I'm not sure whether to expand the brackets on the right hand side, or what values I should move to what side etc. I'm just confused about how to do this question as a whole :/
    I would multiply through to eliminate the fractions then exapnd the brackets. You then need to collect the terms in x.

    Post your working if you get stuck.
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    (Original post by studentdying999)
    I have but I'm not sure whether to expand the brackets on the right hand side, or what values I should move to what side etc. I'm just confused about how to do this question as a whole :/
    Try cross-multiplying (multiplying each side by f and by d) to get rid of the fractions first, then try to collect all the terms containing x on one side of the equation.
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    (Original post by Muttley79)
    I would multiply through to eliminate the fractions then exapnd the brackets. You then need to collect the terms in x.

    Post your working if you get stuck.
    I tried to work it out by moving the d denominator of the first fraction to the right side 'd(2x+2e)' and moved the f denominator to the left side to make 'f(x+c)' then expanded the brackets to make fx+c = 2dx+2e. I then moved the c over to make 2dx+2e -c and finally moved the f and got x = 2dx+2e-c/f but in the answer booklet it says the answer is 'x = 2de-fc/f-2d' - what did I do wrong?
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    (Original post by studentdying999)
    I tried to work it out by moving the d denominator of the first fraction to the right side 'd(2x+2e)' and moved the f denominator to the left side to make 'f(x+c)' then expanded the brackets to make fx+c = 2dx+2e. I then moved the c over to make 2dx+2e -c and finally moved the f and got x = 2dx+2e-c/f but in the answer booklet it says the answer is 'x = 2de-fc/f-2d' - what did I do wrong?
    Actually now I realise I left an x over in the right hand side, but how would I work through this to get it onto the left as well?
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    (Original post by studentdying999)
    I tried to work it out by moving the d denominator of the first fraction to the right side 'd(2x+2e)' and moved the f denominator to the left side to make 'f(x+c)' then expanded the brackets to make fx+c = 2dx+2e. I then moved the c over to make 2dx+2e -c and finally moved the f and got x = 2dx+2e-c/f but in the answer booklet it says the answer is 'x = 2de-fc/f-2d' - what did I do wrong?
    Check expansion of brackets ..

    OK - note that x appears on both sides of your equation:
    fx + fc = 2dx + 2de

    Collect them on the LHS
    fx - 2dx = 2de -fc

    Can you see what to do now?
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    (Original post by studentdying999)
    I tried to work it out by moving the d denominator of the first fraction to the right side 'd(2x+2e)' and moved the f denominator to the left side to make 'f(x+c)' then expanded the brackets to make fx+c = 2dx+2e. I then moved the c over to make 2dx+2e -c and finally moved the f and got x = 2dx+2e-c/f but in the answer booklet it says the answer is 'x = 2de-fc/f-2d' - what did I do wrong?
    Your first step is correct but when you expand brackets, you have to multiply all the terms in the brackets by the term(s) outside it. So you should have fx + fc = 2xd + 2ed . Can you continue from there?
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    (Original post by Muttley79)
    Check expansion of brackets ..

    OK - note that x appears on both sides of your equation:
    fx + fc = 2dx + 2de

    Collect them on the LHS
    fx - 2dx = 2de -fc

    Can you see what to do now?
    Yes, I understand now! Thanks so much
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    (Original post by Sonechka)
    Your first step is correct but when you expand brackets, you have to multiply all the terms in the brackets by the term(s) outside it. So you should have fx + fc = 2xd + 2ed . Can you continue from there?
    I understand now, thank you!
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    (Original post by studentdying999)
    I understand now, thank you!
    Well done for sorting it out
    Thanks for the rep.
 
 
 
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