1. The problem statement, all variables and given/known data The voltage V in a power cable varies sinusoidally with time t. At t = 1, the voltage is 12 volts. The voltage rises to its maximum level of 20 volts by t = 6. At t = 11, the voltage returns to 12 volts and then begins to fall. The minimum voltage is 4 volts. 2. Relevant equations y = (+/-)A*cos(Bx (+/-) C)+D or y = (+/-)A * sin(Bx (+/-) C)+D 3. The attempt at a solution Finding A: The use of (M-m) / 2 yields the amplitude, which is (20-4)/2 = 8. So, A = 8. Finding B: The use of 2pi / B yields the period. So, assuming that the period of the average voltage function is 10 (11-1=10), I have 2pi / B = 10. 2pi=10B 2pi/10 = B pi/5 = B So the period is pi/5. Finding C: Unsure of how to proceed in this step, please advise. Finding D: The use of (M+m)/2 yields the vertical shift, which is (20+4)/2 = 12. So, D or vertical shift in this case is 12. My guess at the equation of this sinusoid is y = -8cos((pi/5)*x + C) + 12. Any assistance is helping me understand how to obtain C would be invaluable to me.