Question 4 need help Thanks Answer true or false and briefly

Question 4 need help. Thanks

Answer true or false, and briefly justify: If for c, d, Z, c divides d and d divides c, then c = plusminus d.

Solution

c divides d

So, d=mc where m is some integer

d divides c so

c=nd hwere n is some integer

So,

d=mc=mnd

d(1-mn)=0

So,

mn=1

Hence, m=n=1

or m=n=-1

Hence proved