Arithmetic and geometric mean

Write a function Mean(x, y) that returns two values for positive $x$ and $y$ at once: the arithmetic mean $\dfrac{x + y}{2}$ and the geometric mean $\sqrt{x y}$. Use it to find the means of the pairs $(a, b)$, $(a, c)$, $(a, d)$ for the numbers $a, b, c, d$.

A single line with four integers $a$, $b$, $c$, $d$ ($1 \le a, b, c, d \le 10^6$).

Three lines: for each pair the arithmetic and the geometric mean, each with exactly 2 digits after the decimal point.

The function returns two results: in Python and Go — return am, gm, in C++ — output parameters (double& am). $x \cdot y$ reaches $10^{12}$ — multiply in long long or double, not in int.

In the first example: $(4, 9)$ — 6.50 6.00, $(4, 16)$ — 10.00 8.00, $(4, 25)$ — 14.50 10.00.