Dummit And Foote Solutions Chapter 10.zip -

Use the relations: ( a \otimes b = a \otimes (b \bmod \gcd(m,n)) ). The result is isomorphic to ( \mathbb{Z}/\gcd(m,n)\mathbb{Z} ). The trick is to show that ( m(a\otimes b) = a\otimes (mb) = a\otimes 0 = 0 ), and similarly ( n ). Hence the tensor product is annihilated by ( \gcd(m,n) ). 11. Projective and Injective Modules (introduction) Definition: ( P ) is projective iff every surjection ( M \to P ) splits. Equivalently, ( \text{Hom}(P,-) ) is exact.

Check closure under addition and under multiplication by any ( r \in R ). For quotient modules ( M/N ), verify that the induced action ( r(m+N) = rm+N ) is well-defined. Dummit And Foote Solutions Chapter 10.zip

( \text{Hom}_R(M,N) ) is only an abelian group, not an ( R )-module, because ( r(f(m)) ) vs ( f(rm) ) conflict. 8. Exact Sequences and Splitting Typical Problem: Prove that ( 0 \to A \xrightarrow{\alpha} B \xrightarrow{\beta} C \to 0 ) splits if and only if there exists a homomorphism ( \gamma: C \to B ) such that ( \beta \circ \gamma = \text{id}_C ). Use the relations: ( a \otimes b =