1.

Show that veca.(vecbxxvec c) is equal in magnitude to the volume of the parallelopiped formed on the three vectors, veca,vecb and vec c

Answer»

Solution :Suppose `VEC(OA)=vecb,vec(OC)=vecc and vec(OE)=VECA` `vecb and vec c` are adjacent sides of parallelogram OABC
Area of `squareOABC,vecS=vecbxxvecc`
`:.Shatn=vecbxxvecc`
where `HATN` unit vector perpendicular to plane form by `vecb and vecc and theta` is angle between `veca and vecS`.
`:.veca.(vecbxxvecc)=veca.vecS [because vecbxxvecc=vecS]`
`=aScostheta`
`=(acostheta)S`
`=hS""......(1)`
where in `DeltaEOE., EE.=h=acostheta`
Suppose VOLUME of parallelepiped OABCDEF is V.
`:.V` = Area of `squareOABCxx` perpendicular (h) of parallelogram OABC from E
`:. V=sh"".....(2)`
From result (1) and (2)
`veca.(vecbxxvecc)=V`


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