Warning This might contain spoilers. 

The move she used to finish Eren was a direct reference to a earlier scene in the anime (this has not been done in th manga as far as I know). At this point in time the viewer does not know Annie is the titan. The fight move used there resembles her fighting moves used during the training. this is one of the clue's beside the face resemblance of the titan to Annie. Some deeper information on this, the move she used is a karate move from the original Kata's. As stated in the video linked she has been trained in martial arts by her father.


How did the Female Titan cut Eren's titan form?
I understand that this is a common question and typically I can solve them, but this one keeps messing me up:

Find the points of intersection (A and B) on the circles $x^2+y^2+4x-10y+20=0$ and $x^2+y^2-4x-2y+12=0$; find the equation of the line $AB$.
