If the apex angle of an isosceles triangle is 30 degrees, what is the base angle?
等腰三角形的顶角是30度，则底角是多少度．
<gadget id="calculator">180 - 30</gadget>
<output>150</output>

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

<result>75</result>