If the equation of the plane passing through the line of intersection of the planes 2x - 7y + 4z - 3 = 0, 3x – 5y + 4z + 11 = 0 and the point (-2, 1, 3) is ax + by + cz - 7 = 0, then the value of 2a + b + c - 7 is.......
If the equation of the plane passing through the line of intersection of the planes 2x - 7y + 4z - 3 = 0, 3x – 5y + 4z + 11 = 0 and the point (-2, 1, 3) is ax + by + cz - 7 = 0, then the value of 2a + b + c - 7 is.......
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1 Answer
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The equation of the plane passing through the line of intersection is:
(2x - 7y + 4z - 3) + λ (3x - 5y + 4z + 11) = 0.
The plane passes through the point (-2, 1, 3).
(2 (-2) - 7 (1) + 4 (3) - 3) + λ (3 (-2) - 5 (1) + 4 (3) + 11) = 0
(-4 - 7 + 12 - 3) + λ (-6 - 5 + 12 + 11) = 0
(-2) + λ (12) = 0 ⇒ 12λ = 2 ⇒ λ = 1/6.
Substitute λ back into the equation:
(2x - 7y + 4z - 3) + (1/6) (3x - 5y + 4z + 11) = 0
Multiply by 6:
6 (2x - 7y + 4z - 3) + (3x - 5y + 4z + 11) = 0
12x - 42y + 24z - 18 + 3x - 5y + 4z + 11 = 0
15x - 47y + 28z - 7 = 0.
This is the equation ax + by + cz - 7 = 0.
So, a=15,...more
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(a – 1) × 2 + (b – 2) × 5 + (g – 3) × 1 = 0
2a + 5b + g – 15 = 0
Also, P lie on line
a + 1 = 2λ
b – 2 = 5λ
g – 4 = λ
2 (2λ – 1) + 5 (5λ + 2) + λ + 4 – 15 = 0
4λ + 25λ + λ – 2 + 10 + 4 – 15 = 0
30λ – 3 = 0
a + b + g = (2λ – 1) + (5λ + 2) + (λ + 4)

Take
x = 2λ + 1, y = 3λ + 2, z = 4λ + 3
= (α − 2)
Now,
(α − 2) ⋅ 2 + (β − 3) ⋅3 + (γ − 4) ⋅ 4 = 0
2α − 4 + 3β − 9 + 4γ −16 = 0
⇒ 2α + 3β + 4γ = 29
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