[填空题]
Two identical water waves pass a sensor in a r jywhi sps.c*5d.i6x.qb (*xn oceano,,nd+k 4x4p v gqdg;ikgraphy laboratory. As the waves pa4,, 4x+ ivpqdgk;ngdkss the sensor, the 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. $D_{min}$ = m $D_{max}$ = m
2.Find the first time after 1616 seconds at which the depth of water reaches 3.5m. t ≈
