Let a, b and c be three unit vectors such that |a-b|²+|a-c|²=8. Then |a+2b|²+|a+2c|² is equal to.
Let a, b and c be three unit vectors such that |a-b|²+|a-c|²=8. Then |a+2b|²+|a+2c|² is equal to.
Asked by Shiksha User
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1 Answer
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|a|=|b|=|c|=1
|a-b|²+|a-c|²=8
⇒|a|²+|b|²-2a.b+|a|²+|c|²-2a.c=8
⇒4-2 (a.b+a.c)=8
⇒a.b+a.c=-2
|a+2b|²+|a+2c|²
=|a|²+4|b|²+4a.b+|a|²+4|c|²+4a.c
=10+4 (a.b+a.c)
=10-8=2
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