Answer
Graphical approximation: $\approx-3.9$
Calculator: $\approx-3.6$
Work Step by Step
(negative direction = clockwise)
For a point on the unit circle, the x-coordinate is $=\cos t$,
the y-coordinate is $\sin t$,
$\displaystyle \tan t=\frac{x}{y}$.
We estimate (see image below)
$\sin t\approx-0.95$
$\cos t\approx 0.28$
Dividing our estimates, $\tan$0.8$=\displaystyle \frac{x}{y}\approx-3.9$
while the calculator shows $\tan$0.8$\approx-3.6$
:
(see image below)
