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Provide solution for RD Sharma Maths Class 12 Chapter 26 Directions Cosines and Direction Ratios Exercise Multiple Choice Question, question 15.

Answers (1)

Final Answer: (a) 2

Hint: Use section formula

Given: Points (3,2,-1) and (6,2,-2) and P(5,y,z)

To Find: y-coordinate of P(5,y,z)

Solution: Let P divide the line joining (3,2,-1)and (6,2,-2) in t:1

Using section formula

\begin{aligned} &(5, y, z)=\left[\frac{t(6)+3}{t+1}, \frac{t(2)+2}{t+1}, \frac{t(-2)+(-1)}{t+1}\right] \\ &(5, y, z)=\left[\frac{6 t+3}{t+1}, \frac{2 t+2}{t+1}, \frac{-2 t-1)}{t+1}\right] \end{aligned}

Comparing x-coordinate

\begin{aligned} &5=\frac{6 t+3}{t+1} \\ &5(t+1)=6 t+3 \\ &t=2 \end{aligned}

Now comparing y-coordinate

\begin{aligned} &y=\frac{2 t+2}{t+1} \\ &y=\frac{2(2)+2}{2+1} \\ &y=2 \end{aligned}

Therefore, y-coordinate of P(5,y,z) is 2. hence option(a) is correct.

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