The bisectors of angles A and B of parallelogram ABCD meet at point F of side CD. Prove that F is the midpoint of CD.

AF is the bisector of ∟А, then ∟КAF = ∟ВAF, ∟ВAF = ∟AFD – as internal criss-crossing at parallel AB and CD and secant AF, so ∟КAF = ∟AFD. ∆ AFD – isosceles, AD = FD. The situation is similar with ∆ ВFC, ВС = FС. ABCD is a parallelogram, therefore AD = BC, therefore FD = FС, F is the middle of CD.



One of the components of a person's success in our time is receiving modern high-quality education, mastering the knowledge, skills and abilities necessary for life in society. A person today needs to study almost all his life, mastering everything new and new, acquiring the necessary professional qualities.