Solution
= Solution
Since $H=(X+Z)/\sqrt2$, the <Hadamard gate> is, up to a <global phase>, the <rotation gate>
$$
e^{-i\pi(X+Z)/(2\sqrt2)}=-iH.
$$
Thus its <Bloch sphere> action is a \b[rotation through $\pi$ about the axis $(1,0,1)/\sqrt2$], halfway between the positive $x$ and $z$ axes:
$$
\boxed{(r_x,r_y,r_z)\longmapsto(r_z,-r_y,r_x).}
$$
The identities $HXH=Z$, $HYH=-Y$ and $HZH=X$ verify this <Bloch vector> transformation directly.