Which values for theta have the same reference angles

What is the vertex form of f(x) = x2 + 6x + 3

In the figure below, ∠dec ≅ ∠dce, ∠b ≅ ∠f, and segment df is congruent to segment bd. point c is the point of intersection between segment ag and segment bd, while point e is the point of intersection between segment ag and segment df. the figure shows a polygon comprised of three triangles, abc, dec, and gfe. prove δabc ≅ δgfe.

Which of the following is best modeled using a linear equation y=ax+b, where a is less than 0?