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vec P and vec Q are two perpendicular ve...

`vec P and vec Q` are two perpendicular vectors. If `vec P = 5 hati +7hatj-3hatk and vec Q=2hati+2hatj-aveck` then the value of a is

A

-5

B

-7

C

`+8`

D

`-8`

Text Solution

Verified by Experts

The correct Answer is:
D
`because vec P bot vec Q therefore vec P cdot vec Q =0`
`vec P cdot vec Q =(5hati + 7hatj -3hatk) cdot (2hati+2hatj -ahatk)`
`=10+14+3a=0`
`therefore 24=-3a" "therefore a=-8`
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