There is an isosceles trapezoid with a base angle of 45**0, an upper base of 8 cm, and a lower base of 12 cm. What is the area of this trapezoid in square centimeters?
有一个等腰梯形，底角为45**0，上底为8厘米，下底为12厘米，这个梯形的面积应是多少平方厘米．
<gadget id="calculator">8 + 12</gadget>
<output>20</output>

<gadget id="calculator">12 - 8</gadget>
<output>4</output>

<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">2 / 2</gadget>
<output>1</output>

<gadget id="calculator">20 * 1</gadget>
<output>20</output>

<result>20</result>