(1)CF=DE=x,CD=FE=100/x,y=30x+80(x+100/x+100/x)+500=30x+80x+16000/x+500=110x+16000/x+500,CD<DE,x*DE>CD*DE,x2>100,x>10,x<AB,x<21x的取值范围:10(米)<x<21(米);(2)y=110x+16000/x+500,3000=110x+16000/x+500,3000x=110x2+16000+500x110x2-2500x+16000=011x2-250x+1600=0△=(-250)2-4*11*1600<0 |