L and M are two points with position vectors 2→a−→b and →a+2→b respectively. Write the position vector of a point N which divides the line segment LM in the ratio 2 : 1 externally.
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Solution
−−→OL=2→a−→b and −−→OM=→a+2→b Since N divides LM in 2:1 externally, so −−→ON=1.−−→OL−2.−−→OM1−2=2.(2→a−→b−1.(→a+2→b)) Therefore, −−→ON=3→a−4→b