1. Let the tangent lines $M A$ and $M B$ through the point $M(4,2)$ to the circle $C: x^{2}+y^{2}=10$ touch the circle at points $A$ and $B$. Find the length of the minor arc between points $A$ and $B$.
(提示: 弦 $A B$. 所在直线的 equation is $2 x+y$ $=5$, the distance from the circle center to this line is $\sqrt{5}$, thus $\angle A O B=$ $90^{\circ}$, the length of the minor arc between the tangent points $A 、 B$ is $\frac{\sqrt{10} \pi}{2}$.)