[填空题]
Two identical water waves pass a sensor in an oceanography laboradg dnl, wzauzy9 ,pi/2+lx3.itory. As the w+*u3qi o-gqfb 0db xh o.z-u1x5+gtvkaves pass the sensor, the depth, D, in metrebo t+z1.qiu g -+do vh3 gkuxfq*0bx-5s, 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 ≈
