If M is the point of intersection of diagonals AC and BD, then M is the midpoint of AC and BD.
ok the ques is -
The points A,B,C in R^3 are position vectors
a=(1,1,2) b=(2,-1,4) c=(2,1,5)
a) write down the vectors AB and AC
b) Hence or otherwise find the position vector of the point D such that ABCD is a parallelogram.
i solved for
a) AB=(1,-2,2) and AC=(1,0,3)
b) ok the answer differs from my answer but this is what i said -
using the definition of vector addition,
DC + AD = AC
-(1,-2,3) + (x,y,z) =(1,0,3)
(x,y,z) = (2,-2,5)
am i incorrect for ques (b)??
the answer was different!