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Provide solution for RD Sharma maths class 12 chapter 26 Direction Cosines and Direction Ratios exercise Fill in the blanks question 18

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Final Answer  →-\frac{3}{7}
Hint :

In zx plane y-coordinate is zero and y coordinate of points divide line segment.
Given :  

Points are (2,3,1) \text { and }(6,7,1)
To find:

 Ratio in which line is divided
Solution :

Let zx-plane  divide the line segment in ratio

                                \left(m_{1}\right) \quad\quad\quad\quad\left(m_{2}\right)

                                p\quad \quad\quad\quad\quad\quad\quad1

            (2,3,1)\quad\quad\quad\quad (x, 0, z)\quad\quad\quad\quad (6,7,1)

        \left(x_{1}, y_{1}, z_{1}\right) \quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\left(x_{2}, y_{2}, z_{2}\right)

                                            \text { zx plane }

Using section formula,

\begin{aligned} &y=\frac{m_{1} y_{2}+m_{2} y_{2}}{m_{1}+m_{2}} \\\\ &0=\frac{7 p+3}{p+1} \end{aligned}

\begin{aligned} &7 p+3=0 \\\\ &p=\frac{-3}{7} \end{aligned}

Therefore, the zx plane divide the line in ratio \frac{-3}{7}

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