3. Linear Taylor Series Approximation

The Taylor series expansion for g=sqrt(f) around the point f=1 is:

  g = 1 + (f-1)*(1/2) - ((f-1)*(f-1)/2)*(1/4) + ...

Using just the first two terms:

  g = 0.5 + f*0.5

This approximation is exact for f=1 and too high for f<1 and f>1.