If the apex angle of an isosceles triangle is 100°, what is the base angle of the triangle?
一个等腰三角形的顶角是100°，这个三角形的底角是多少度．
<gadget id="calculator">180 - 100</gadget>
<output>80</output>

<gadget id="calculator">80 / 2</gadget>
<output>40</output>

<result>40</result>