#### Answer

$F(0)=0$
This means that the fraction of the moon's face illuminated by the sun is zero.

#### Work Step by Step

$F(t)=\frac{1}{2}(1-\cos t)$
For $F(0)$, the phase angle $t=0$. Substituting $t=0$ in the equation,
$F(0)=\frac{1}{2}(1-\cos 0)$
$F(0)=\frac{1}{2}(1-1)$
$F(0)=\frac{1}{2}(0)$
$F(0)=\frac{1}{2}(0)$
$F(0)=0$
This means that the fraction of the moon's face illuminated by the sun is zero.