[填空题]
A land surveyor is measuring the area of2af711qttusf/0,d ntchlo1 e a trianguamro2 )-fh f8ywav(qsvxnd/6w;/ s q,lar plot of land on a smooth hill. She uses a theodolite to determine the coordinat,a nfv/(h-y)2rd mvq xqa6s8;/ swwfoes of the corners of the land and finds them to be (-8,20,10),(16,8,7) and (-20,-8,3) , where the coordinates are in metres from a fixed origin where she stands.
Using vectors, determine the area of the land. $m^2$
