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    Complete the square for the expressions:

    3x2-x

    I tried doing this but got stuck a bit.

    3(x2-1/2)2-(1/2)2

    based on (x2+b/2)2-(b/2)2 the x2=3 and bx=-1 right? or am I wrong here?



    PS: missed the first week cause i switched schools and I'm behind a week's worth of lessons

    Thanks in advance
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    (Original post by KK.Violinist)
    Complete the square for the expressions:

    3x2-x

    I tried doing this but got stuck a bit.

    3(x2-1/2)2-(1/2)2

    based on (x2+b/2)2-(b/2)2 the x2=3 and bx=-1 right? or am I wrong here?



    PS: missed the first week cause i switched schools and I'm behind a week's worth of lessons

    Thanks in advance
    When you take the 3 out of the bracket, you've divided x^2 by 3 but not the -x. Try taking the 3 out of the bracket before you try completing the square and see how you do.
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    So would it be like this?

    3(x2-1/3x)-(1/3)2

    if it is that, then what about the equation since it has to be 2 for the denominator? Sorry, this is the part where I'm confused.
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    (Original post by KK.Violinist)
    So would it be like this?

    3(x2-1/3x)-(1/3)2

    if it is that, then what about the equation since it has to be 2 for the denominator? Sorry, this is the part where I'm confused.
    Hi,

    Take it step by step.

    3x^2 - x can be written as 3(x^2 - x/3).

    Next complete the square for the bit in brackets, not forgetting to multiply it all by 3.
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    ok so;

    3(x-x/3/2)2

    and this makes it 3(x-1/6)2?
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    (Original post by KK.Violinist)
    So would it be like this?

    3(x2-1/3x)-(1/3)2

    if it is that, then what about the equation since it has to be 2 for the denominator? Sorry, this is the part where I'm confused.
    It may be easier to think of it like this:
    Let me give you another example. Suppose you have

    x^2 - 5x.

    To complete the square would mean doing:
    (x-(5/2))^2 - (5/2)^2. This is because when we expand the first bracket we end up with x^2 - 5x + (5/2)^2 and to get rid of the last term we minus (5/2)^2.

    If instead we have something like:

    6x^2 - 2x - 5, the steps would look like this:

    6x^2 - 2x - 5
    = 6(x^2 - x/3 - 5/6)
    = 6((x - 1/6)^2 - (1/6)^2 - 5/6)) (NOTE 1/3 divided by 2 is 1/6).

    In the last line make sure you multiply it all by 6. Also note that to make it easier first minus out the (1/6)^2 term (which leaves us with x^2 - x/3) and then minus 5/6 (to get x^2 - x/3 - 5/6, which when multiplied by 6 gives the original equation).

    Hope this helps!

    You can ask if something doesn't make sense!
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    I think I've cracked it haha.

    3x^2-x

    3(x^2-(x/3)/2)

    3(x-1/6)^2-(1/6)^2 since x=1

    3(x-1/6)^2-1/36
    times by 3
    3(x-1/6)^2-1/12
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    (Original post by KK.Violinist)
    I think I've cracked it haha.

    3x^2-x

    3(x^2-(x/3)/2)

    3(x-1/6)^2-(1/6)^2 since x=1

    3(x-1/6)^2-1/36
    times by 3
    3(x-1/6)^2-1/12
    I can see what you are doing but some of your working is confusing and each step needs to be equal to the previous step - see how the other poster set it out.

    You can always check these by expanding again.
 
 
 
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