If the apex angle of an isosceles triangle is 30°, what is the base angle of the triangle?
一个等腰三角形的顶角是30°，则这个三角形的底角是多少°．
<gadget id="calculator">180 - 30</gadget>
<output>150</output>

<gadget id="calculator">150 / 2</gadget>
<output>75</output>

<result>75</result>