1) in first place you need to Know what kind of figure is it, in order to find solve the problem, as you can see it is a parallelogram, and the condition for this geometric figure the opposites are equal ,
2) if you have a non -rectangular parallelogram and draw a diagonal from A to C, you obtain two equal triangles, for this reason the line AC IS CALLED DIAGONAL, and divide the parallelogram
3) in first place to determine that the angles are congruents for two triangles the Diagonal is comun for both, and the vertex ∡CAB IS THE SAME ∡ACD
4) If the diagonal AB AND CD are equal , AD AND BC are equal too, then the triangles are congruent
5) segment AB Parallel to CD THEY HAVE THE SAME SLOPE AND MAGNITUDE