What is the base angle of an isosceles triangle whose apex angle is 30°?
顶角是30°的等腰三角形，它的一个底角是多少°．
<gadget id="calculator">180 - 30</gadget>
<output>150</output>

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

<result>75</result>