This initial value occurs when the sine value is increasing and it will reach its maximum value of 1 when Sin(πt/6) = Sinπ/2, that is when t = 3. Consequently, monthly sales exceed 100,000 during the period between t = 1.1884 and 4.8116 [3 - 1.1884 = 1.8116 so the other extreme occurs at 3 + 1.8116]
Note : on the basis of these calculations, January is 0 ≤ t < 1 : February is 1 ≤ t < 2 :....May is 4 ≤ t < 5 So the period when sales exceed 100,000 occurs between Feb 6 and May 25 and annually thereafter.</span>