C2 - Practical Trig Equation Watch

thats_my_poison
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#1
Report Thread starter 12 years ago
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H = 12 cos(30t) + 10. Find the first two times when h = 19; find the maximum and minimum values of H. I’ve set out my working for the first part of the question but im stuck on the second part:

19 = 12 cos(30t) + 10
0.75 = cos 30t
30t = 41.41, 318.59
t = 1.38, 10.62

Are these answers correct and how do you find the max/min values of H?
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gyrase
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(Original post by alison_141288)
H = 12 cos(30t) + 10. Find the first two times when h = 19; find the maximum and minimum values of H. I’ve set out my working for the first part of the question but im stuck on the second part:

19 = 12 cos(30t) + 10
0.75 = cos 30t
30t = 41.41, 318.59
t = 1.38, 10.62

Are these answers correct and how do you find the max/min values of H?
Those answers are correct.

You differentiate H and set dH/dt = 0 and solve to get t values. Sub these t-values into the original H equation to get H values.
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thats_my_poison
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(Original post by Dev.420)
Those answers are correct.

You differentiate H and set dH/dt = 0 and solve to get t values. Sub these t-values into the original H equation to get H values.
how do you differentiate H = 12 cos(30t) + 10
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gyrase
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(Original post by alison_141288)
how do you differentiate H = 12 cos(30t) + 10
oh right this is C2

well in that case, note that -1 < cos(30t) < 1, so sub cos(30t) = 1, to get max of H; H = 22, and sub cos(30t) = -1, to get min of H;
H = -2.
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M1N1
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Sry, just saw the last post, nm.
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thats_my_poison
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well we've been given a revision check list and one of the topics are 'pratical trig questions' and it gave this question as an example, but i think the teacher prob just wrte down some random numbers as an example
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