If the vertex angle of an isosceles triangle is 120°, then how many degrees is one of the acute angles?
一个等腰三角形的顶角是120°，那么其中一个锐角是多少度．
<gadget id="calculator">180 - 120</gadget>
<output>60</output>

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

<result>30</result>