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

$d=-2.9$ m

We substitute $t=0.4$ in the equation and then solve for $d$: $d=4\tan 2\pi t$ $d=4\tan 2\pi (0.4)$ $d=4\tan (2\pi \times0.4)$ $d=4\tan 0.8\pi$ Since $\tan 0.8\pi=-0.72654$; $d=4\tan 0.8\pi$ $d=4(-0.72654)$ $d=-2.9062\approx-2.9$ Therefore, for $t=0.4$ seconds, $d=-2.9$ m.