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Can't seem to be able to complete the square for this? watch

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    Part b) specifically.

    I did 2x^2 + 8x + 3 = (x+2)^2 - 4 + (3/2)
    = (x+2)^2 - (5/2)

    That is apparently incorrect.
    The answer is 2(x + 2)^2 - 5

    I don't understand how that was achieved though. I see it like this:
    2(x^2 +4x + (3/2))

    2((x + 2)^2 - 4 + (3/2)), which is practically the same?
    How else do I do this?

    And can anyone explain to me why 2(x^2 +4x + (3/2)) is the same as just x^2 + 4x + (3/2) ? I mean surely they're not equal, the first one is x2 the second one, but I was taught that doing so to an equation is fine?
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    (Original post by frostyy)
    ...
    Do you agree that you can write 4 = 2\times 2? i.e: you can pull a factor of 2 out?

    So for example, when you're given 2x^2 + 8x + 3 = (2 \times x^2) + (2 \times 4x) + (2 \times \frac{3}{2}) you can then pull the common factor of 2 out to get you 2(x^2 + 4x + 3/2).

    Then you complete the square on the inside: 2((x+2)^2 -4 + 3/2) = 2((x+2)^2 -5/2) = 2(x+2)^2 - 2 \times \frac{5}{2} = 2(x+2)^2 - 5.

    Which step don't you understand in here?
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    Try arranging 2x^2 + 8x into p(x+q)^2

    2(x+2)^2 which is equal to 2(x^2 + 4x + 4).

    If you expand that it becomes 2x^2 + 8x + 8, then you have to find what r is equal to to make +8 equal to +3
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    (Original post by Zacken)
    Do you agree that you can write 4 = 2\times 2? i.e: you can pull a factor of 2 out?

    So for example, when you're given 2x^2 + 8x + 3 = (2 \times x^2) + (2 \times 4x) + (2 \times \frac{3}{2}) you can then pull the common factor of 2 out to get you 2(x^2 + 4x + 3/2).

    Then you complete the square on the inside: 2((x+2)^2 -4 + 3/2) = 2((x+2)^2 -5/2) = 2(x+2)^2 - 2 \times \frac{5}{2} = 2(x+2)^2 - 5.

    Which step don't you understand in here?
    Oh right, sorry. I just left it in the form 2((x+2)^2 - (5/2)) and got confused.

    Anyway, cheers, I really appreciate your help in all the topics that I post on this website, I really do. Hope Jesus will give you many women, you deserve them.
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    (Original post by frostyy)
    Oh right, sorry. I just left it in the form 2((x+2)^2 - (5/2)) and got confused.

    Anyway, cheers, I really appreciate your help in all the topics that I post on this website, I really do. Hope Jesus will give you many women, you deserve them.
    Yay! Glad that cleared things up. Cheers, mate - don't worry about it.
 
 
 
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