An isosceles triangle, one of its base angles is 45°, what is its apex angle?
一个等腰三角形，它的一个底角是45°，那么它的顶角是多少．
<gadget id="calculator">45 * 2</gadget>
<output>90</output>

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

<result>90</result>