Can someone show me how to get the period for the following equation using radian mode in the calculator?:

d(t) = 2.5 sin0.166 pi (t - 1.5) + 13.4

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Answer - 12.2

The variable following the sine function tells you the frequency f. Forget the -1.5 term -- that is just a phase angle.

2 pi f t = 0.166 pi t
(When f*t incresaes by 1, the phase changes by 2 pi)
Therefore 2f = 0.166
f = 0.083 s^-1
P = 1/f = 1/0.083 = 12.0 s