If the equation $x^2 + y^2 + 2gx + 2fy + 1 = 0$ represents a pair of lines,then

  • A
    $g^2 - f^2 = 1$
  • B
    $f^2 - g^2 = 1$
  • C
    $g^2 + f^2 = 1$
  • D
    $f^2 + g^2 = \frac{1}{2}$

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