If three consecutive vertices of a parallelogram are A(4,3,5), B(0,6,0),C(−8,1,4) and D is the fourth vertex then the angle between AC↔ and BD↔ is

In the figure E is mid point of AC and BD∴E=-2,2,92 Since it is also midpoint BD, we have D=(−4,−2,9)D.r’s of AC are (12, 2, 1)D.c’s of AC are 12149,2149,1149D.r’s of BD are (-4, -8, 9)D.c’s of BD are −4161,−8161,9161Angle between diagonals  θ=Cos−155149161