[填空题]
Two identical water waves pass a sensor in an oceanob-rijwj(x1 4o /*uggigraphy laboratorygtw(ni 8uig g*l)r8w5. As the waves pass the sensor, thig(n)8g l *5wruw igt8e depth, D, in metres, of water is recorded and modelled by the function
D(t)=3.21−0.45cos($24.2^{\circ}$$\times$t)
where t is the elapsed time, in seconds, since the first wave hit the sensor.
1.Find the minimum and maximum depths of the water as the two waves pass the sensor.$D_{min}$ = ; $D_{max}$ =
2.Find the first time after 1616 seconds at which the depth of water reaches 3.5m. t ≈
