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Math Help - Changing the subject of formua with squares and roots

  1. #1
    Junior Member
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    Derbyshire, central UK
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    Changing the subject of formua with squares and roots

    I have tried answering the following question by squaring everything (I think), but I am not right.

    c = \sqrt{a^2+b^2} (Change the subject of
    the formula to a)

    My try:

    c^2 = (a^2)^2+(b^2)^2

    c^2 = a^4+b^4

    a^4 = c^2-b^4

    a = sqrt[4]{c^2-b^4}

    Can you see my error please?
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  2. #2
    MHF Contributor
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    West Malaysia
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    Quote Originally Posted by Meggomumsie View Post
    I have tried answering the following question by squaring everything (I think), but I am not right.

    c = \sqrt{a^2+b^2} (Change the subject of
    the formula to a)

    My try:

    c^2 = (a^2)^2+(b^2)^2

    c^2 = a^4+b^4

    a^4 = c^2-b^4

    a = sqrt[4]{c^2-b^4}

    Can you see my error please?

    HI

    you are correct by squarring both sides to get rid of the square root but you worked it out wrongly .

    (c)^2=(\sqrt{a^2+b^2})^2

    c^2=a^2+b^2

    a^2=c^2-b^2

     <br />
a=\sqrt{c^2-b^2}<br />
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  3. #3
    Junior Member
    Joined
    Aug 2009
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    Derbyshire, central UK
    Posts
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    Dohh!!! Yes, I see that now!!! Thanks.
    Last edited by Meggomumsie; September 27th 2009 at 09:06 AM. Reason: I have put new question in a new thread
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