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प्रश्न
Write the value of `vec a .(vecb xxveca)`
उत्तर
Let:
`vec a=a_1hati+a_2hatj+a_3hatk`
`vecb=b_1hati+b_2hatj+b_3hatk`
`therefore veca.(vecb xx veca)`
`=(a_1hati+a_2hatj+a_3hatk).[(b_1hati+b_2hatj+b_3hatk) xx (a_1hati+a_2hatj+a_3hatk)]`
`=(a_1hati+a_2hatj+a_3hatk).[(b_2a_3-b_3a_2)hati-(b_1a_3-b_3a_1)hatj+(b_1a_2-b_2a_1)hatk]`
`=(b_2a_3-b_3a_2)a_1-(b_1a_3-b_3a_1)a_2+(b_1a_2-b_2a_1)a_3`
`=a_1a_3b_2−a_1a_2b_3−a_2a_3b_1+a_1a_2b_3+a_2a_3b_1−a_1a_3b_2`
Alternate Method:
`vec b xx vec a` is a vector perpendicular to both `veca and vecb`
`∴ vecb xx veca ⊥ veca` and `vecb xx veca ⊥ vecb`
⇒ `veca . (vecb xx veca)=0`
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