Xiao Min made a fan, the maximum opening angle is 90° after opening, the width of the drawing paper part is 20 cm, and the width of the blank part is 40 cm, what is the minimum area of paper needed to paste this fan? Overlapping pasted parts are not considered.
小敏做了一把扇子，打开后最大张角为90°，其中画纸部分宽度为20厘米，空白部分宽度为40厘米，求糊这把扇子至少要用多少面积的纸？不考虑重叠粘贴部分．
<gadget id="calculator">20 + 40</gadget>
<output>60</output>

<gadget id="calculator">60 ** 2</gadget>
<output>3_600</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">3.14 * 3_600 * (1/4)</gadget>
<output>2_826</output>

<gadget id="calculator">40 ** 2</gadget>
<output>1_600</output>

<gadget id="calculator">3.14 * 1_600 * (1/4)</gadget>
<output>1_256</output>

<gadget id="calculator">2_826 - 1_256</gadget>
<output>1_570</output>

<result>1_570</result>