=∑P(5,n,51)cosa1+Q(5,n,)cos月 i=1 +R(5;,7,51)c0sy;|AS =∑P(5,m,51)AS)2+Q(5,n,5△S) +R(5;,m,5)(△S) 牛3.取极限→0取极限得到流量的精确值 上页i i i i i i i i i n i i i i i R S P Q +  =  + = ( , , )cos ] [ ( , , )cos ( , , )cos 1             i i i i x y yz i i i i x z n i i i i i R S P S Q S ( , , )( ) [ ( , , )( ) ( , , )( ) 1 +  =   +  =          3.取极限  → 0取极限得到流量的精确值