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Need solution for RD Sharma Maths Class 12 Chapter 27 Straight Line of Space Excercise Fill in the blanks Question 10

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Answer :    -\frac{10}{7}

Hint :      Use vector dot product and vector equation of line.

Given :    \begin{aligned} &\frac{x-1}{-3}=\frac{y-2}{2 k}=\frac{z-3}{2} \text { and } \frac{x-1}{3 k}=\frac{5-y}{-1}=\frac{6-z}{5} \\ & \end{aligned}

              \text { let } \overrightarrow{\mathrm{b} 1}=-3 \hat{\imath}+2 \mathrm{k} \hat{\mathrm{j}}+2 \hat{k} \text { and } \overrightarrow{\mathrm{b} 2}=3 \mathrm{k} \hat{\imath}+\hat{\jmath}-5 \hat{k}

              \overrightarrow{\mathrm{b} 1} \cdot \overrightarrow{\mathrm{b} 2}=0   as the lines are at right angle

            \begin{aligned} &-9 k+2 k-10=0 \\ & \end{aligned}

            -7 k=10 \\

                 k=-\frac{10}{7} 

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