What is the length of the arc subtended by a central angle of 90 degrees to the circumference of the entire circle?
90度圆心角所对的弧长占整个圆周长的多少
<gadget id="calculator">90 / 360</gadget>
<output>1/4 = around 0.25</output>

<result>1/4 = around 0.25</result>