Simplify
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By Sophie Germain identity, we know that a 4 + 4 b 4 = ( a 2 + 2 b 2 − 2 a b ) ( a 2 + 2 b 2 + 2 a b ) = ( a ( a − 2 b ) + 2 b 2 ) ( a ( a + 2 b ) + 2 b 2 ) .
All factors are of the form x 4 + 4 , so using the identity with a = 1 , 3 , 5 , 7 , … and b = 1 we get:
[ ( 1 ( 1 − 2 ) + 2 ) ( 1 ( 1 + 2 ) + 2 ) ] [ ( 5 ( 5 − 2 ) + 2 ) ( 5 ( 5 + 2 ) + 2 ) ] … [ ( 9 7 ( 9 7 − 2 ) + 2 ) ( 9 7 ( 9 7 + 2 ) + 2 ) ] [ ( 3 ( 3 − 2 ) + 2 ) ( 3 ( 3 + 2 ) + 2 ) ] [ ( 7 ( 7 − 2 ) + 2 ) ( 7 ( 7 + 2 ) + 2 ) ] … [ ( 9 9 ( 9 9 − 2 ) + 2 ) ( 9 9 ( 9 9 + 2 ) + 2 ) ]
All factors cancel except the first in the denominator and the last in the numerator yielding a value for the fraction of 1 0 0 0 1