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    rb23's Avatar
    rb23 Posts: 6, Reputation: 1
    New Member
     
    #1

    Mar 27, 2010, 12:54 PM
    To find the coordinates of the focus of a given conic equation...
    This question appeared in my practise exam and I didn't have a clue of how to go about it... here goes...

    If S (a,b) represents the coordinates of the focus for conic x^2 + 2xy + y^2 +2x + 4y = 0, then the maximum value of |a|.b is
    a) 1
    b) 2
    c) 3
    d) 4

    It'd be great if someone would help me with the solution and provide me with a detailed explanation... thanks
    galactus's Avatar
    galactus Posts: 2,271, Reputation: 282
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    #2

    Mar 27, 2010, 03:09 PM

    Solving for y, we get:



    Find the derivative and set to 0. Solve for x.Sub back in to find the y coordinate.

    These correspond to (a,b).

    Then, plug them into |a|*b to find the max value.
    rb23's Avatar
    rb23 Posts: 6, Reputation: 1
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    #3

    Mar 28, 2010, 04:17 AM

    Thank You very much...

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