# Chapter 3 - Review Exercises - Page 137: 66c

$F(\pi)=1$ 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.

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