(1)S=
(2)6400.
(1)根据题意得
S=
即S=
(2)①当1≤t≤30,t∈N时,S=-(t-20) 2+6400,
当t=20时,S的最大值为6400;
②当31≤t≤50,t∈N时,S=-90t+9000为减函数,
当t=31时,S的最大值是6210,
∵6210<6400,∴当t=20时,日销售额S有最大值6400.
(1)S=
(2)6400.
(1)根据题意得
S=
即S=
(2)①当1≤t≤30,t∈N时,S=-(t-20) 2+6400,
当t=20时,S的最大值为6400;
②当31≤t≤50,t∈N时,S=-90t+9000为减函数,
当t=31时,S的最大值是6210,
∵6210<6400,∴当t=20时,日销售额S有最大值6400.