Hello
We have to prove: (a-b) * (a+b) = 2 * (a*b) where a and b are two vectors.
Now, (a-b) * (a+b) = a*a - b*a + a*b - b*b
= 0 - b*a + a*b - 0 [Beacuse a vector multiplied by a vector itself is 0]
= a*b + a*b [Because (a*b) = -(b*a)]
= 2 * (a*b)
Hence proved!
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