Conflict
Find the value of a such that the points with position vectors are co-planar. Vectors are:
3 i + 6 j + 9 k
1 i + 2 j + 3 k
2 i + 3 j + k
4 i + 6 j + a k
# Source: all india c.b.s.e. 2017 maths paper.
The answer is 2.
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1 solution
This question was not in my set (3) . From which set was this from?
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how was ur ppr ? i'm expecting 94-98 what abt u ?
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I am expecting 98-100 (If any marks are cut , then it would silly mistakes)
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@Saharsh Rathi – same goes for me ........ no apparent mistakes by me as such .
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@A Former Brilliant Member – How was your physics paper ? Mine did not go well. I was not sure about the Cherbonyl disaster , and one derivation and there were couple of silly mistakes too.
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@Saharsh Rathi – that one went well too again expecting 95-98 , I was not sure about the Cherbonyl disaster too but guessed as the only thing in +2 syllabus which can cause mass destruction are radiation derivation saari aati thi.
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@A Former Brilliant Member – Hmm.. best of luck for chemistry
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@Saharsh Rathi – thnx buddy :) bol to u too ...
The first 3 vectors are already co-planar since their box product is zero. ( 3 vectors are co-planar if their box product = 0 )
So if box product of 2nd , 3rd , 4th = 0 then all 4 vectors will become co-planar. i.e. ∣ ∣ ∣ ∣ ∣ ∣ 1 2 4 2 3 6 3 1 a ∣ ∣ ∣ ∣ ∣ ∣ = 0
4 ( − 7 ) − 6 ( − 5 ) + a ( − 1 ) = 0
a = 3 0 − 2 8 = 2