F' (A) = cos 2 A – sin 2 A = cos 2A f' (A) = 0 cos 2A = 0 2A = π / 2 A = π / 4 f'' (A) = – 2 sin 2A = – 2 sin (π / 2) = – 2 negative f (A) is maximum at π / 4 The maximum value is cos (π / 4) sin (π /180° π1 150° 5π/6√ 3 /2 135° 3π/4√ 2 /2 1° 2π/31/2 90° π/2 0 60° π/3 1/2 45° π/4 √ 2 /2 30° π/6 √ 3 /2 0° 0 1 See also Cosine function;Cos (2π) cos (2 π) 2π 2 π is a full rotation so replace with 0 0 cos(0) cos (0) The exact value of cos(0) cos (0) is 1 1
2
