#### Answer

$F(\pi)=1$
This means that the whole of the moon's face is illuminated by the sun.

#### Work Step by Step

$F(t)=\frac{1}{2}(1-\cos t)$
For $F(\pi)$, the phase angle $t=\pi$. Substituting $t=\pi$ in the equation,
$F(\pi)=\frac{1}{2}(1-\cos \pi)$
$F(\pi)=\frac{1}{2}(1-(-1))$
$F(\pi)=\frac{1}{2}(1+1)$
$F(\pi)=\frac{1}{2}(2)$
$F(\pi)=1$
This means that the whole of the moon's face is illuminated by the sun.