In an isosceles triangle, the base angle is 70 degrees, what is the apex angle?
等腰三角形中，底角是70度，顶角是多少度？
<gadget id="calculator">70 * 2</gadget>
<output>140</output>

<gadget id="calculator">180 - 140</gadget>
<output>40</output>

<result>40</result>