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Two adjacent sides of a parallelogram AB...

Two adjacent sides of a parallelogram ABCD are given by `vec(AB)=2hati+10hatj+11hatk` and `vec(AD)=-hati+2hatj+2hatk`. The side AD is rotated by an acute angle `alpha` in the plane of the parallelogram so that AD becomes AD'. If AD' make a right angle withe the side AB then the cosine of the angle `alpha` is given by

A

`(8)/(9)`

B

`(sqrt(17))/(9)`

C

`(1)/(9)`

D

`(4sqrt(5))/(9)`

Text Solution

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The correct Answer is:
B
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