A triangle is both an isosceles triangle and an obtuse triangle. The ratio of its two interior angles is 1:4. What is the apex angle of this triangle?
一个三角形，既是等腰三角形，又是钝角三角形，它的两个内角度数的比是1：4，这个三角形的顶角是多少°．
<gadget id="calculator">1 + 1 + 4</gadget>
<output>6</output>

<gadget id="calculator">4 / 6</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">180 * (2/3)</gadget>
<output>120</output>

<result>120</result>