There are 10 points in the plane, how many line segments are there that end at 2 points?
平面内有10个点，以其中每2个点为端点的线段共有多少条？
<gadget id="calculator">1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9</gadget>
<output>45</output>

<result>45</result>