
HCF and LCM
Suppose that x, y in R*\U(R) that is x,y are nonzero, nonunit in R, where R is UFD. Let x = u.{p_1^(a_1)....p_t^(a_t)}
y = v{p_1^(b_1)....p_t^(b_t)}
where a_i and b_i >= 0 , 1=<i=<t and u,v are in U(R).
Let c_i =max{a_i , b_i} and d_i = min{a_i , b_i}.
Show that HCF{x,y} and LCM{x,y} exist and
HCF{x,y} = (x,y) = p_1^(d_1).....p_t^(d_t)
LCM{x,y} = [x,y] = p_1^(c_1).....p_t^(c_t)
Deduce that (x,y)[x,y] = xy
How do you approach to this problem
Thank you very much

Use your definitions, prove for example, that $\displaystyle (x,y) \vert x$ and $\displaystyle (x,y) \vert y$ and any other $\displaystyle z$ such that $\displaystyle z \vert x$ and $\displaystyle z \vert y$ we have $\displaystyle z\vert (x,y)$. Do the analogue for $\displaystyle [x,y]$. You should note however that $\displaystyle (x,y)[x,y]\sim xy$ (the equality doesn't necesarily hold) because you have to take into account the units $\displaystyle u$ and $\displaystyle v$.