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secondary 4 | A Maths
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must i assume that abc are positive ? what if they happen to be negative ? will i get 2 sets of answers ?
why a has to be -4 :
if the graph starts from 0300, then it should be increasing (upward sloping) from 0300.
I.e the coefficient of cos(bt) should be positive. So -a has to be positive, which means a has to be negative
Try plotting T(t) = -4(π/1200 t - π/4) + 30
Using b = π/12 implies that the temperature fluctuates too rapidly throughout the day
The question says t is the time in hours. So at 3am, it would be 0300 hours, i.e t = 300. At 3pm, it would be 1500 hours, i.e t = 1500.
't is the number of hours elapsed from 0300 hours of the present day'
Anyway, the way t is equated in the parts of the question also don't make sense.
We never see things like 't = 0300' in Cambridge papers. t is variable of a value ,not a clock reading , similar to your mentioning of interpreting 3am as a reading and not hours.
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