Trig: graphs and equations question Watch

tenki
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I am confused at this question:

The minimum depth, d ft, of water in a harbor t hours after midnight can be approximated by the function
\qquad\qquad d(t) = 35 + 15cos0.5t \quad where \quad 0 \leq t \leq 24
A ship with a draught of 25 ft is in harbor at midnight. By what time must it leave to prevent grounding?

I don't understand what draught exactly means, even after googling. Seeing there was a value, I set d(t) = 25 and solved for t:

35 + 15cost0.5t = 25
15cost0.5t = -10
0.5t = cost^{-1}(-10/15)
t=263.620...

The answer is 4.36am. I've tried sketch a graph and looking at it but it makes no sense. I need a few pointers please!
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Kvothe the Arcane
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(Original post by tenki)
I am confused at this question:

The minimum depth, d ft, of water in a harbor t hours after midnight can be approximated by the function
\qquad\qquad d(t) = 35 + 15cos0.5t \quad where \quad 0 \leq t \leq 24
A ship with a draught of 25 ft is in harbor at midnight. By what time must it leave to prevent grounding?

I don't understand what draught exactly means, even after googling. Seeing there was a value, I set d(t) = 25 and solved for t:

35 + 15cost0.5t = 25
15cost0.5t = -10
0.5t = cost^{-1}(-10/15)
t=263.620...

The answer is 4.36am. I've tried sketch a graph and looking at it but it makes no sense. I need a few pointers please!
Are you working in radians?
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tenki
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(Original post by keromedic)
Are you working in radians?
No, why do you ask?
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Kvothe the Arcane
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(Original post by tenki)
No, why do you ask?
You should be.
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