In an isosceles triangle, if the measure of the top angle is 72°, what is the measure of the base angle?
在一个等腰三角形中，已知顶角的度数是72°，则一个底角的度数为多少．
<gadget id="calculator">180 - 72</gadget>
<output>108</output>

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

<result>54</result>