The apex angle of an isosceles triangle is 40 degrees, what is the base angle of this isosceles triangle?
一个等腰三角形的顶角是40度，求这个等腰三角形的底角？
<gadget id="calculator">180 - 40</gadget>
<output>140</output>

<gadget id="calculator">140 / 2</gadget>
<output>70</output>

<result>70</result>