a) Let f:N*N->Q be defined by f(m,n)=(m-3)/n. Determine if f is injective or surjective.

b) Show that if f:A->B and g:B->C are both bijective, then the composition (g o f):A->c is also bijective.

Solve the recurrence relations

a(r)-5a(r-1)+6a(r-2)=2^r+r

(r,r-1,r-2 are all subscripts)