Points of a finite projective line

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The discussion focuses on computing fractions in the finite field GF(23), specifically how 2/5 and 18/22 both yield the result of 5. The calculations demonstrate that in GF(23), 2 multiplied by its multiplicative inverse of 5 results in 5, as shown by the equation 5 × 5 = 25 ≡ 2 (mod 23). Similarly, 18/22 also simplifies to 5 through the equation 5 × 22 = 110 ≡ 18 (mod 23). This illustrates the properties of finite fields, particularly when the field order is a prime number.

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Lapidus
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I found in Thompson "From Error-Correcting to Sphere Packing and Simple Groups" this on page 131

upload_2016-9-14_9-58-29.png


How do you compute m/n in a finite field?

Take the equivalence class 5 given above. Why does 2/5 and 18/22 give 5?

thanks
 
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The finite field being used is ##GF(23)## which is (isomorphic to) the set of integers modulo 23. Because 23 is prime, that is a field.

2/5=5 because ##5\times 5=25=2\mod 23##
18/22=5 because ##5\times 22=110=18\mod 23##

If you are operating in a finite field of prime order ##p##, the multiplicative inverse of ##f## is the smallest positive solution ##x## of the equation ##xf=1+kp## for ##k## any non-negative integer.
 
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