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Math Help - Factorise

  1. #1
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    Factorise

    Factorise y4 - 3y^2 - 4. Hint. Let z = y^2
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  2. #2
    MHF Contributor harish21's Avatar
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    Quote Originally Posted by AJShaw View Post
    Factorise y4 - 3y^2 - 4. Hint. Let z = y^2
    y^4 - 3y^2 -4 = (y^2)^{2} - 3y^2 -4

    if z=y^2, your problem becomes:

    z^2 - 3z -4

    Try factorizing now
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  3. #3
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    I am just learning factorising. Is it:

    z^2-3z-4

    z^2-3z-4

    z-3-4

    z-7

    If not right, can you show me how to do it please?
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  4. #4
    MHF Contributor harish21's Avatar
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    Quote Originally Posted by AJShaw View Post
    I am just learning factorising. Is it:

    z^2-3z-4

    z^2-3z-4

    z-3-4 : How did you get this?

    z-7

    If not right, can you show me how to do it please?
    What you have done is not right. Please review your class notes/book about factorizing!

    z^2-3z-4

    = z^2-(4-1)z - 4

    = z^2 - 4z + z - 4

    = z(z-4) + 1(z-4)

    =(z+1)(z-4)

    Now substitute the value of z that you had assumed at the beginning of the quesiton.
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