a) luna piena
1/2 * (1 - cos @) = 1
1 - cos @ = 2
cos @ = 1 - 2
@ = arccos(-1) = pi
b) mezza luna
1/2 * (1 - cos @) = 1/2
1 - cos @ = 1
cos @ = 1 - 1 = 0
@ = pi/2
c) analogamente
1/2 * (1 - cos @) = 3/4
1 - cos @ = 3/2
cos @ = 1 - 1/2
@ = arccos (-1/2) = 2/3 pi V 4/3 pi