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Mathematics · 2025 · 3 marks
CBSE 2025 · Region 4 · Set 1 · Q30
Find the distance of the point (-1,-5,-10) from the point of intersection of the lines (x -1)/2=(y -2)/3=(z -3)/4 and (x -4)/5=(y -1)/2= z.
Find the distance of the point $\displaystyle (-1,-5,-10)$ from the point of intersection of the lines $\displaystyle \frac{\mathrm{x}-1}{2}=\frac{\mathrm{y}-2}{3}=\frac{\mathrm{z}-3}{4}$ and $\displaystyle \frac{\mathrm{x}-4}{5}=\frac{\mathrm{y}-1}{2}=\mathrm{z}$.
Marking-scheme solution
\[\begin{aligned}
& l_{1}: \frac{\mathrm{x}-1}{2}=\frac{\mathrm{y}-2}{3}=\frac{\mathrm{z}-3}{4}=\lambda \\
& \text { Any point on } l_{1} \text { is }(2 \lambda+1,3 \lambda+2,4 \lambda+3) \\
& l_{2}: \frac{\mathrm{x}-4}{5}=\frac{\mathrm{y}-1}{2}=\frac{\mathrm{z}-0}{1}=\mu \\
& \text { Any point on } l_{2} \text { is }(5 \mu+4,2 \mu+1, \mu) \\
& \text { For point of intersection, } \\
& 2 \lambda+1=5 \mu+4,3 \lambda+2=2 \mu+1 \\
& \text { Solving, } \lambda=\mu=-1 \\
& \text { Since, } \lambda=\mu=-1 \text { satisfy } 4 \lambda+3=\mu \\
& \therefore \text { Point of intersection is }(-1,-1,-1) \\
& \text { Now distance of }(-1,-5,-10) \text { from }(-1,-1,-1) \text { is: } \\
& \sqrt{(-1+1)^{2}+(-1+5)^{2}+(-1+10)^{2}}=\sqrt{97} \text { units }
\end{aligned}
\]
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