If a triangle has an axis of symmetry and the largest angle is 120°, what is the smallest angle of the triangle?
一个三角形有一条对称轴，最大角为120°，那么这个三角形最小的一个角是多少度．
<gadget id="calculator">180 - 120</gadget>
<output>60</output>

<gadget id="calculator">60 / 2</gadget>
<output>30</output>

<result>30</result>