Define $u_n$ and $v_n$ inductively

Question

it is asked to find an expression for $u_{n}$ in terms of n and for $v_{n}$ also in terms of n

$a, b \in $R

$v_1=(a+b)/2$

$u_1=\sqrt{ab}$

$u_{n+1}= \sqrt{u_n\cdot v_n}$

$v_{n+1}=\dfrac{v_n+u_n}{2}$

i have tried to start calculating a list of $u_n$ and $v_n$ but i found no linking between terms.

Thanks!