What is the maximum number of points of intersection of 10 straight lines drawn in the same plane?
在同一平面内画10条直线最多可有多少个交点．
<gadget id="calculator">0 + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9</gadget>
<output>45</output>

<result>45</result>