[填空题]
The temperature in Nern91 spa+ *wabw York ranges from. e5-: q.5 bat(xnujcl uv7xjy $-4^{\circ}C$ to $22^{\circ}C$ throughout the course of a year. The temperature, T, can be modelled by the function
$T(t) = -a\cos(bt)+d$,
Where t is time measured in months from the beginning of the year, and a, b and $d \in \mathbb{Z}^{+}$.
1.Show that
1.a=13;
2.b=30;
3.d=9.
2.Sketch the function T(t) for $0 \leq t \leq 12$, clearly labelling the coordinates of the maximum and minimum points.
3.Find the temperature when t=4. $^{\circ}C$
4. 1.Determine the number of months in a year that the temperature is above $9^{\circ}C$.
2.Find the probability that on a randomly chosen day of the year, the temperature is above $9^{\circ}C$.
5.If the temperature in New York ranged from $-7^{\circ}C$ to $25^{\circ}C$ instead of $-4^{\circ}C$ to $22^{\circ}C$, describe how this would affect the probability found in (d) part (ii).
