(1)由题意有502= k 100 ,解得k=25×104,∴P= 25×104 x = 500 x ,∴总利润L(x)=x? 500 x ?1200? 2x3 75 =? 2x3 75 +500 x ?1200(x>0);(2)由(1)得L′(x)=? 2 25 x2+ 250 x ,令L′(x)=0? 250 x = 2 25 x2,令