The geometric mean’s just the square root of the product, here.
So, sqrt(2X) = 8
shift from the left to the right of the equals sign doing the opposite action on the right to get x on its own. A square root when shifted over is a square.
Shifting that square root over, 2x = 8^2 and thus 2x=64.
Doing the same trick to get x on its own on the left, 2 multiplies on the left and so divides on the right: we get x=64/2 and doing that division gives us our answer:
x=32.