Question

find area of triangle abc & triangle def if D E F are mid points of AB BC &CA D(2,1) E(1,0) F(_1,3)

Answer 1

Find the area of DEF in the usual way, as, for example

http://www.mathopenref.com/coordtrianglearea.html

Since DEF is 1/2 the size of ABC, the area of ABC is 4 times the area of DEF.