(a/L2, -b/L2, -c/L2, -d/L2),
where L2 = length squared = (a*a + b*b + c*c + d*d).
This is the multiplicative inverse, i.e., (a,b,c,d)*(a/L2, -b/L2, -c/L2, -d/L2) = (1,0,0,0).
public bool Invert()
Public Function Invert As Boolean
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