In an isosceles triangle, its base angle is 70°, what is its apex angle?
在一个等腰三角形中，它的底角是70°，它的顶角是多少度．
<gadget id="calculator">70 * 2</gadget>
<output>140</output>

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

<result>40</result>