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-   -   To find the coordinates of the focus of a given conic equation... (https://www.askmehelpdesk.com/showthread.php?t=460749)

  • Mar 27, 2010, 12:54 PM
    rb23
    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
  • Mar 27, 2010, 03:09 PM
    galactus

    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.
  • Mar 28, 2010, 04:17 AM
    rb23

    Thank You very much...

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