Chapter 4 - Graphs of the Circular Functions - Section 4.3 Graphs of the Tangent and Cotangent Functions - 4.3 Exercises - Page 168: 47c

$d=-12.3$ m

We substitute $t=0.8$ in the equation and then solve for $d$: $d=4\tan 2\pi t$ $d=4\tan 2\pi (0.8)$ $d=4\tan (2\pi \times0.8)$ $d=4\tan 1.6\pi$ Since $\tan 1.6\pi=-3.07768$; $d=4\tan 1.6\pi$ $d=4(-3.07768)$ $d=-12.311\approx-12.3$ Therefore, for $t=0.8$ seconds, $d=-12.3$ m.