In an isosceles triangle, its apex angle is 72°, what is its base angle?
一个等腰三角形，它的顶角是72°，它的底角是多少度．
<gadget id="calculator">180 - 72</gadget>
<output>108</output>

<gadget id="calculator">108 / 2</gadget>
<output>54</output>

<result>54</result>