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If A=[i-2j-3k], B=[2i+j-k], find [A*B] |
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Answer» Answer: Given: a =2 i ^ + j ^
−3 k ^ and b =3 i ^ −2 j ^
− k ^
a . b =(2 i ^ + j ^
−3 k ^ )(3 i ^ −2 j ^
− k ^ ) =6−2+3=7....(1) ∣ a ∣= 2 2 +1 2 +(−3) 2
=
....(2) ∣ ∣ ∣ ∣
b
∣ ∣ ∣ ∣
= 3 2 +(−2) 2 +(−1) 2
= 14
....(3) cosθ= ∣ a ∣. ∣ ∣ ∣ ∣
b
∣ ∣ ∣ ∣
a . b
= 14
14
7
= 2 1
cosθ=cos60 o
θ=60 o
Hence the required angle is 60 o
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