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Please Solve R.D. Sharma class 12 Chapter 22 Algbra of Vectors  Exercise Very Short Answer Question 10 Maths textbook Solution.

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Answer: \frac{\vec{a}+\vec{b}+\vec{c}}{3}

Hint: You must know the rules of vector functions

Given: If \vec{a}+\vec{b}+\vec{c}are position vectors of vertices of a triangle, then write the position vector of centroid.

Solution: Let ABC be a triangle and D,E and F are the mid-points of sides BC, CA and AB respectively.

Also, Let \vec{a}+\vec{b}+\vec{c}are position vectors of A, B, C respectively.                          

Then position vectors of D, E and F are                                             

                \left(\frac{\vec{b}+\vec{c}}{2}\right) \cdot\left(\frac{\vec{c}+\vec{a}}{2}\right),\left(\frac{\vec{a}+\vec{b}}{2}\right) respectively.                                                            

The position vector of a point divides AD in the ratio of 2 is                                        

        

\frac{1 \cdot \vec{a}+2\left(\frac{\vec{b}+\vec{c}}{2}\right)}{3}=\frac{\vec{a}+\vec{b}+\vec{c}}{3}

 

Similarly, position vectors of the points divides BE, CF in the ratio of 2:1 are equal to

 

            \frac{\vec{a}+\vec{b}+\vec{c}}{3}

Thus, the points dividing AD in ratio 2:1 also divides BE, CF in the ratio.

Hence, medians of triangle are concurrent and the position of centroid is \frac{\vec{a}+\vec{b}+\vec{c}}{3}

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