If one base angle of an isosceles triangle is 45 degrees, what is its top angle?
一个等腰三角形的一个底角是45度，它的顶角是多少度．
<gadget id="calculator">45 * 2</gadget>
<output>90</output>

<gadget id="calculator">180 - 90</gadget>
<output>90</output>

<result>90</result>