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bearing in mind, "t" is in years, 6months is just 1/2 year
solve for "r", you'd get a decimal amount, multiply times 100, to get the percentage form
The cross product of two vectors gives a third vector 
that is orthogonal to the first two.
Normalize this vector by dividing it by its norm:
To get another vector orthogonal to the first two, you can just change the sign and use
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Normalize this vector by dividing it by its norm:
To get another vector orthogonal to the first two, you can just change the sign and use