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  • Please solve RD Sharma Class 12 Chapter 26 Directions Cosines and Direction Ratio Exercise Multiple Choice Question, question 8  Maths textbook solution.

Please solve RD Sharma Class 12 Chapter 26 Directions Cosines and Direction Ratio Exercise Multiple Choice Question, question 8  Maths textbook solution.

Answers (1)

Answer: (b) 3:1 externally

Hint: Use of section formula

Given: Points (1,2,3) and (4,2,1)

To find: Ratio in which xy plane divides the point

Solution: Let the xy plane divides the given point in the ratio t:1

 

Using section formula the point of intersection are:

(x, y, z)=\left[\frac{t(4)+1}{t+1}, \frac{t(2)+2}{t+1}, \frac{t(1)+3}{t+1}\right]

The z-coordinate of any point of xy plane is zero.

\begin{aligned} &\Rightarrow \frac{t(1)+3}{t+1}=0 \\ &\Rightarrow t+3=0 \\ &\Rightarrow t=-3 \\ &\Rightarrow t: 1=-3: 1 \end{aligned}

Therefore, the xy plane divide the given points in 3:1 externally. Hence option (b) 3:1 externally is correct.

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