题目

An 11-year-old boy's dance in the rain in Lagos, Nigeria, not only touched the hearts of millions who saw his passion but it is helping make his dream come true.Those who saw Anthony Madu jumping high and pirouetting（作单脚尖旋转）without shoes on the rain-soaked street in a video posted by his dance teacher were in awe（敬畏）of his talent—So much so that the attention the young ballet dancer, received online earlier this summer has helped him obtain a scholarship from a prestigious ballet, company in New York City.With the support of actress Viola Davis, who shared Anthony's v如图，正方形ABCD内接于⊙O，若正方形的边长等于4，求图中阴影部分面积．