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NCERT Class XII Mathematics Chapter - - Solutions

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Question : 71 of 78
Marks: +1, -0
Find the coordinates of the point where the line through (3, – 4, – 5)and (2, – 3, 1) crosses the plane 2x + y + z = 7.
Solution:  
The equation of the line through (3, –4, –5) and (2, –3, 1) is x31=y+41=z+56\frac{x-3}{-1}=\frac{y+4}{1}=\frac{z+5}{6} ...(1)
Any point on (1) is (3 – k, – 4 + k, – 5 + 6k) ...(2)
This point lies on 2x + y + z = 7
∴ 2 (3 – k) + (– 4 + k) + (–5 + 6k) = 7
⇒ 6 – 2k – 4 + k – 5 + 6k = 7
⇒ 5k = 10 ⇒ k = 2
Putting in (2), the required point is (3 –2, – 4 + 2, – 5 + 12) i.e. (1, – 2, 7)
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