This is a theorem about Jacobi symbols in my textbook:

Let n and m be ODD and positive. Then (a/nm)=(a/n)(a/m) and (ab/n)=(a/n)(b/n)

Moreover,

(i) If gcd(a,n)=1, then ( ) = 1 = ( )

(ii) If gcd(ab,nm)=1, then ( )=(a/n)

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(i) is easy and follows from the definition, but how can we prove (ii)? My textbook stated the theorem without proof and just says the proofs are easy, but I have no idea why (ii) is true.

Any help is appreciated!