设漏斗高为h,底面半径是r
h²+r²=20²
h²+(r²/2)+(r²/2)
圆锥体积是v=(1/3)πr²h
v²=(π²/3)×r²×r²×h²
=(π²/12)×(r²/2)×(r²/2)×h²