If the vectors AB=3i^+4k^ and AC=5i^−2j^+4k^ are the sides of a triangle ABC, then the length of the median through A is
(A)72
(B)33✓ Correct
(C)45
(D)18
Answer: (B)
Solution
The median from A runs to the midpoint of BC, and in vector form AM=2AB+AC. Adding the given vectors, AM=2(3i^+4k^)+(5i^−2j^+4k^)=4i^−j^+4k^, whose length is 16+1+16=33.
JEE Main · 2013 · 07 Apr 2013 · Offline · Single correct option