physics vectors

Question

Figure shows three vectors a,b and c, where R is the midpoint of PQ. Then which of the following relations is correct

need solution for 8th question

Answer 1

need clear solution for 11th question

Comments

This is the answer for 11th question http://www.sarthaks.com/3588/vectors-physics

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but i didn't understand what you did in 11th question

Answer 2

The correct relation is  (A) i.e vector a+b=2c

From figure, Diagonals of a parallelogram bisect each other.

We know If two vectors acting simultaneously on a particle are represented in magnitude and direction by the two adjacent sides of a parallelogram drawn from a point, then their resultant is completely represented in magnitude and direction by the diagonal of that parallelogram drawn from that point.