Q53 / 90 · JEE Main 2022 (29 Jul Shift 1) · Mathematics

Let a line with direction ratios a,-4 a,-7 be perpendicular to the lines with direction ratios 3,-1,2b and b, a,-2. If the point of intersection of the line x+1a2+b2=y-2a2-b2=z1 and the plane x-y+z=0 is α,β,γ, then α+β+γ is equal to ________.

Correct answer: 10

Solution

Given a line with direction ratios a,-4 a,-7 be perpendicular to the lines with direction ratios 3,-1,2b and b, a,-2. If the point of intersection of the line x+1a2+b2=y-2a2-b2=z1 and the plane x-y+z=0 is α,β,γ, then α+β+γ is equal to ________.

Now given a,-4a,-7⊥ to 3,-1,2b

So, 3a+4a-14b=0

⇒a=2b     ⋯i

Also a,-4a,-7⊥ to b,a,-2

So, ab-4a2+14=0     ⋯ii

From Equations i and ii we get,

2b2-16b2+14=0

⇒b2=1

So, a2=4b2=4

So, line becomes x+15=y-23=z1=k

Let points be α=5k-1,β=3k+2,γ=k

As α,β,γ satisfies plane x-y+z=0

So, 5k-1-3k+2+k=0

⇒k=1

∴ α+β+γ=9k+1=10

Hence, the correct answer is 10.

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