[填空题]
The water depth, D, i871i 8 mvfdk;j0rf8a1j57aeptw0sf mj;s agyn metres, in a harbour on a particular day can be mod74nlryf6yra: rzc)x .ke as78ca m4,xq2fut9elled by the equatio8 y7r4tkcaxmae.42fucy,9 qs lazn6r xr 7f: )n
D=2.5cos($30^{\circ}$$\times$t)+5, 0≤t≤24,
where t is the elapsed time, in hours, since midnight.
1.Draw the graph of D versus t on the grid below.
2.Find the lowest and highest depths of water in the harbour, and the times when they occur. $D_{min}$ = t = ; $D_{max}$ = t =
3.A large yacht has a draught of 3 metres. Decide whether the yacht will be able to enter the harbour at 5 pm.
