An isosceles triangle has a top angle of 90 degrees and a base angle of 90 degrees.
一个等腰三角形，顶角是90度，一个底角是多少度．
<gadget id="calculator">180 - 90</gadget>
<output>90</output>

<gadget id="calculator">90 / 2</gadget>
<output>45</output>

<result>45</result>