Bound on the angle between a vector and a subspace

Question

Suppose you have three complex vectors $x_1$, $x_2$, and $x_3$. Define $a = \angle(x_1,x_2)$, $b = \angle(x_1,x_3)$. My question is about $c = \angle(x_1, span(x_2,x_3))$, the angle between the vector $x_1$ and the subspace spanned by the two vectors $x_2$ and $x_3$. Is there any lower or upper bound on the angle $c$ in terms of $a$ and $b$?