Explain the triangle angle sum property

Which expression gives you the distance between the points (5,1)and(9,-6)

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.

What is the 9th term in the geometric sequence described by this explicit formula? an=-6. (2)(n-1) apex