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Maths yr2 trig help

https://www.revisely.com/alevel/maths/edexcel/pure-questions/trigonometry/trigonometric-identities-2/6
I’m stuck on 6c), this is my work so far:

cos(15t - a) = -1
15t - a = 180°

So should I use my previous value of a, and solve for t? But the question explicitly asks for f(t) first…? Any help is welcomed. Thank you!!
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Original post by mihyeb
https://www.revisely.com/alevel/maths/edexcel/pure-questions/trigonometry/trigonometric-identities-2/6
I’m stuck on 6c), this is my work so far:

cos(15t - a) = -1
15t - a = 180°

So should I use my previous value of a, and solve for t? But the question explicitly asks for f(t) first…? Any help is welcomed. Thank you!!

For c) youre only interested in the min value of 3sin+4cos, so its almost a write down using part a) or pythagoras on 3,4. Then for d) youd want the time at which it occurs so 15t-a=180 as you say, using "a" from part a).
(edited 4 months ago)

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