0) Area of the base square: ${\displaystyle A_{0}=1}$
1) Area of the inscribed quarter circle: ${\displaystyle A_{1}={\frac {\pi \cdot r_{1}^{2}}{4}}={\frac {\pi }{4}}\cdot s_{0}\approx 0.785}$
B) Area of black color: ${\displaystyle B=A_{0}-A_{1}=1-{\frac {\pi }{4}}\approx 0.215}$

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