... get a a 4 4 a 4 55 4a Similarly, 55 4b b2 Adding these two inequalities, a a b b a a a a 5 4a 2 Third solution Applying the AM – GM Inequality we get b 5 4b b b b 5 1 a 2 1 b3 2 a b 5 a b ... 4 c3 33 Adding these three inequalities, a b c a b c 4 a.a.a b.b.b c.c.c a a a b b b c c c 4 Third solution Applying the AM – GM Inequality we get a b 1 a 1 c 1 a b c 1 b c a b c Therefore, ... sin i i i sin 7 ,i 1, 2, ,5 It is easy to show that 1 Therefore, 5 cos a2 b c2 d e2 f 2 cos 100 a, b, c 0, a b c , a a b c 3 a b b c c2 27 31 Solution Applying the AM – GM Inequality we get...