Answer:
Explanation:
3.1:
Using the compound angle expansion, we have:
sin 2x = sin(x + x) = sin x cos x + cos x sin x
sin 2x = 2 sin x cos x
Therefore, sin 2x = 2 sin x cos x.
3.2:
Using the result from 3.1:
3.2.1: sin 100° = 2 sin 50° cos 50° = sin 100° = 0.766
3.2.2: sin 46° = 2 sin 23° cos 23° = sin 46° = 0.719
3.2.3: sin 40° = 2 sin 20° cos 20° = sin 40° = 0.642
3.3:
Using the identity sin(a ± b) = sin a cos b ± cos a sin b:
3.3.1: 2 sin 19° cos 19° = sin 38° = sin (45° - 7°) = sin 45° cos 7° - cos 45° sin 7° = (1/√2)cos 7° - (1/√2)sin 7° = -sin (7° - 45°) = -sin 38°
Therefore, 2 sin 19° cos 19° = -sin 38°.
3.3.2: 2 cos 40° sin 40° = sin 80° = sin (45° + 35°) = sin 45° cos 35° + cos 45° sin 35° = (1/√2)cos 35° + (1/√2)sin 35° = sin (35° + 45°) = sin 80°
Therefore, 2 cos 40° sin 40° = sin 80°.
3.3.3: sin 25° cos 155° = (1/2)(sin 180°) = 0
Therefore, sin 25° cos 155° = 0.