The sum of the top angle and one base angle of an isosceles triangle is 135°, what is its top angle?
一个等腰三角形的顶角与一个底角的和是135°，它的顶角是多少度．
<gadget id="calculator">180 - 135</gadget>
<output>45</output>

<gadget id="calculator">135 - 45</gadget>
<output>90</output>

<result>90</result>