下图显示了一个在正方形内画的圆。圆内又画了一个阴影正方形。 阴影部分占整个图形的几分之几？ 答：___

1. Express the area of the outer square in terms of the circle's radius

Let the radius of the circle be $r$.
The circle is inscribed in the outer square, so the side length of the outer square is equal to the diameter of the circle, which is $2r$.
Area of outer square = $(2r)^2 = 4r^2$.

2. Express the area of the inner shaded square in terms of the circle's radius

The inner shaded square is inscribed in the circle, so its diagonal is equal to the diameter of the circle, which is $2r$.
Area of inner square = $\frac{1}{2} \times \text{diagonal}_1 \times \text{diagonal}_2 = \frac{1}{2} \times (2r) \times (2r) = 2r^2$.

3. Calculate the fraction of the figure that is shaded

Fraction shaded = $\frac{\text{Area of inner square}}{\text{Area of outer square}} = \frac{2r^2}{4r^2} = \frac{1}{2}$.