A. Let "I" be an ideal in a commutative ring "R", if a,b∈R then a+I=b+I if and only if a≡b(modI) particularly, a+I=I if and only if a∈I
b. Suppose R=Z[x] and I the principal ideal (x^2+x+1) if a=3+2x and b=4+3x Show that (a+I)(b+I)=ab+I
c. Show that R/I is a commutative ring where I is an ideal of a commutative ring I