$x^2 - 2x - 15 = $

$12x^2y^2 - 7xy + 49x^2y^2 = $

$4x^2 + 12xy + 9y^2 = $

$x^2 - 4x + 5 = $

$25x^2 - 16y^2 = $

$x^2 + 8x + 15 = $

$9a^2 + 6a + 1 = $

$6xy^3 - 12xy^2 = $

$a^2 - 2a - 15 = $

$a^2 + 2a - 18 = $

$x^2 - y^2 = $

$x^2 + 5x + 4 = $

$\frac{x^2}{9} + \frac{1}{3}x + \frac{1}{3} = $