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Algebra question.

  • 12-10-2020 9:40pm
    #1
    Registered Users Posts: 20


    Can somebody please explain this one to me.

    I need to isolate Z. I have been given the solution as it is a practice test but I don't get the second line (marked with a star). Also, the final result as given does not tally with any of the multiple choice answers supplied.


    1. What is happening where starred? I would have multiplied both sides by x+root whatever, but supplied solution doesnt.
    2. Given final line is solution supplied, why does it not match any of the given answers.
    Thank you.


Comments

  • Registered Users Posts: 6,039 ✭✭✭The Continental Op


    Caveat - I've not done any algerbra in 45 years.

    Without looking at the working out or answers I did it myself and got to the answer in the solution given so that seems to be right but I can't for the life of me find any one of the answers that fits?

    Where you star is I got to that stage by multiplying both sides by (x+√Z) and then dividing both by (r-2)

    Wake me up when it's all over.



  • Registered Users Posts: 20 dublinstudent.


    Caveat - I've not done any algerbra in 45 years.

    Without looking at the working out or answers I did it myself and got to the answer in the solution given so that seems to be right but I can't for the life of me find an one of the answers that fits?


    So what is happening on the second line with the star? To remove the 1/xxxx on the right , multiply both sides by xxxx, but he didnt, and it now has 1/whatever on the left........


  • Registered Users Posts: 6,039 ✭✭✭The Continental Op


    So what is happening on the second line with the star? To remove the 1/xxxx on the right , multiply both sides by xxxx, but he didnt, and it now has 1/whatever on the left........

    See above

    Wake me up when it's all over.



  • Moderators, Regional South Moderators Posts: 5,710 Mod ✭✭✭✭Quackster


    The answer bottom left is exactly the same as A, just written differently.


  • Registered Users Posts: 1,457 ✭✭✭jogdish


    Looks like A), the solution while correct has not been expressed as a single fraction. Make a common fraction of the r-2 on the bottom and it should be (doing it in my head) it.


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  • Registered Users Posts: 6,039 ✭✭✭The Continental Op


    Quackster wrote: »
    The answer bottom left is exactly the same as A, just written differently.

    Don't see that but be delighted if you can explain how the worked answer is the same? The old brain needs a workout occasionally.

    Wake me up when it's all over.



  • Moderators, Regional South Moderators Posts: 5,710 Mod ✭✭✭✭Quackster


    So what is happening on the second line with the star? To remove the 1/xxxx on the right , multiply both sides by xxxx, but he didnt, and it now has 1/whatever on the left........
    The equation has been inverted. If X = 1/Y, then 1/X = Y. You can just flip the equation over.


  • Moderators, Regional South Moderators Posts: 5,710 Mod ✭✭✭✭Quackster


    Don't see that but be delighted if you can explain how the worked answer is the same? The old brain needs a workout occasionally.

    As previous poster says, 1/(R-2) - X = (1 - RX + 2X)/(R-2) as you multiply -X by R-2 to create a single fraction.


  • Registered Users Posts: 3,826 ✭✭✭ozmo


    They flipped both sides - you can do that.
    so
    1/2 = 1/x
    becomes
    2/1 = x/1 (and x = 2

    in your case (r-2)/1 becomes 1/(r-2) and the other side becomes something/1

    “Roll it back”



  • Registered Users Posts: 6,039 ✭✭✭The Continental Op


    Quackster wrote: »
    As previous poster says, 1/(R-2) - X = (1 - RX + 2X)/(R-2) as you multiply -X by R-2 to create a single fraction.


    OK got there in the end :D

    Wake me up when it's all over.



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  • Registered Users Posts: 244 ✭✭Pythagorean


    Tricky enough !! I found ABCD hard going, as regards the starred line, a numerical example may help;
    3= 1/1/3 therefore

    1/1/3=3/1 ( or if 1/a =b then 1/b =a)

    Hope this helps !!


  • Closed Accounts Posts: 6,751 ✭✭✭mirrorwall14


    Walk through P1 explaining the star


  • Closed Accounts Posts: 6,751 ✭✭✭mirrorwall14


    Walkthrough P2


    Current post primary maths teacher.

    You can do the same thing to both sides of an equation always (we used to just learn the outcome of doing that step, we now show it)

    You need to be able to find a common denominator to make the answer ‘look’ correct


  • Registered Users Posts: 20 dublinstudent.


    So, some interesting ideas there. Will print it all out and try to follow and understand your explanations.
    It is great you all answered at such a late hour. Thank you.


  • Closed Accounts Posts: 6,751 ✭✭✭mirrorwall14


    So, some interesting ideas there. Will print it all out and try to follow and understand your explanations.
    It is great you all answered at such a late hour. Thank you.

    Hope you got sorted. I can do a quick walkthrough video at some stage for it if you need it.


  • Registered Users Posts: 20 dublinstudent.


    Hope you got sorted. I can do a quick walkthrough video at some stage for it if you need it.
    I need to sit down with a clear head and review this. Thank you for the offer.


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