1.

सिद्ध करें कि `(vec(a)-vec(b))xx(vec(a)+vec(b))=2(vec(a)xxvec(b))`.

Answer» `L.H.S.=(vec(a)-vec(b))xx(vec(a)+vec(b))`
`=vec(a)xxvec(a)+vec(a)xxvec(b)-vec(b)xxvec(a)-vec(b)xxvec(b)" "["वितरण नियम से"]`
`=vec(a)xxvec(b)-vec(b)xxvec(a)" "[because vec(a)xxvec(a)=vec(0)" तथा "vec(b)xxvec(b)=vec(0)]`
`=(vec(a)xxvec(b))+(vec(a)xxvec(b))" "[because-(vec(b)xxvec(a))=(vec(a)xxvec(b))]`
`=2(vec(a)xxvec(b))`.


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