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W(t) models the daily water level  at a pond in Arizona, t days after the hottest day of the year. Here, t is entered in radians.

W(t) = 15cos( 2π/ 3652 t)+43

What is the first time after the hottest day of the year that the water level is 30 cm

 Jan 28, 2019
edited by kikidylm  Jan 28, 2019

I think the function might be


y =15 cos [ (2pi/365) t ] + 43


The water level is at a max at day 0  =  58 cm


The water level is at 30 cm about 153 days after this



I used x for t   here :




cool cool cool 

 Jan 28, 2019

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