The correct one should be
Shadow area =2* semicircle area -2*( 1/3 semicircle area)+equilateral triangle area with side length as radius.
= area of circle -65438+ 0/3 area of circle+area of equilateral triangle with radius.
The method of finding the triangle area may have been learned in primary school, that is: base * height /2.
The key high value is 2√3, which may be beyond the scope of primary schools.