.
D(t) = 75 - degrees.
The amplitude 10 is half the difference 85-65.
75 degrees is the mean temperature, and it happens precisely at midnight - so the sine function has no time shift.
The period is 24 hours.
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PLEASE pay ATTENTION that the sign before the sine function in my post is " - " (MINUS), as it should be,
in opposite to the post by @htmentor, where the sign before the sine function is " + ", which is WRONG.
It is of significant IMPORTANTCY (!)
In this problem, to miss these signs has the same effect as to miss a day and a night.