[问答题]
The water depth, D, in met
j)3sl f 4ck,wbres, in a harbour on a particular day can b
ph ww;ykq ;me,ry9p*-e modelled by the
;pyry,;9q k-wpm * ehw equation
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.
3.A large yacht has a draught of 3 metres. Decide whether the yacht will be able to enter the harbour at 5 pm.