Let a → = i ^ + α j ^ + 3 k ^ and b → = 3 i ^ - α j ^ + k ^ . If the area of the…

Let a=i^+αj^+3k^ and b=3i^-αj^+k^. If the area of the parallelogram whose adjacent sides are represented by the vectors a and b is 83 square units, then a·b is equal to ___ .

Solution

a=i^+αj^+3k^

b=3i^-αj^+k^

area of parallelogram =|a×b|=83.

a×b=i^j^k^1α33-α1=i^4α-j^-8+k^-4α

|a×b|=64+32α2=83

2+α2=6α2=4

a·b=3-α2+3=2

Asked in: JEE Main 2021 (25 Feb Shift 2)

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