解:∵△ABC绕点A顺时针旋转45°得到△A′B′C′,∠BAC=90°,AB=AC= 2 ,∴BC=2,∠C=∠B=∠CAC′=∠C′=45°,∴AD⊥BC,B′C′⊥AB,∴AD= 1 2 BC=1,AF=FC′= 2 2 AC′=1,∴图中阴影部分的面积等于:S△AFC′-S△DEC′= 1 2 ×1×1- 1 2 ×( 2 -1)2= 2 -1.故答案为: 2 -1.