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Vector Algebra

Question
CBSEENMA12035915

Find the position vector of a point R which divides the line joining two points P and Q whose position vectors are   2a + b   and   a - 3b  respectively, externally in the ratio 1:2. Also, show that P is the midpoint of the line segment R.

Solution

Position vector of P is  2a +b Position vector of Q is  a -3b 

Point R divides the lines segment PQ externally in a ratio of 1 : 2 .

Position vector of R = 1 ( a -3b ) -2 (  2a +b ) 1 - 2                               =  a -3b - 4a - 2b1 - 2                               = 3a +5b

Now, we need to show that P is the mid-point of RQ.

So, position vector of P =  position vector of R +  position vector of Q2                                     =  3a + 5b  +  a - 3b 2                                     =   2a +b = Position vector  ( given )

Hence proved.