[填空题]
The tip of a large wind turbine's blade evl7i n9;tw617y k zpu8voei;rotates at a /d-7qqfth1oo- og, fg constant speed on a windy day. Its heiff q1qoh og,d7t/ og--ght, H , in metres, above the ground is modelled by the function
H(t)=52sin($60^{\circ}\times$t)+80,
where t is the elapsed time, in seconds, since the turbine was accelerated to its max speed.
1.Write down the minimum height of the blade's tip above the ground. $H_{min}$ =
2.Find the height of the blade's tip above the ground after 8 seconds.H(8 )≈
3,Find the time it takes for the blade's tip to complete one full revolution.
