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Prove that (veca-vecb)xx(veca+vecb)=2(ve...

Prove that `(veca-vecb)xx(veca+vecb)=2(vecaxxvecb)`.

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`(veca-vecb)xx(veca+vecb)=(veca-vecb) xxveca+(veca-vecb)xxvecb` [ By distributivity of vector product over addition]
`= vecaxxveca-vecbexxveca+vecaxxvecb-vecbxxvecb` [ Again , by distributivity of vector product over addition ]
`=vec0 +vecaxxvecb+vecaxxvecb-vec0`
`= 2vecaxxvecb`
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