Question

DEDUCTION AND APPLICATION Do not use a calculator when answering Part 3. 3.1 Apply the compound angle expansion sin(x + y) = sin x cos y + cos x sin y to expa sin 2x and simplify your answer: sin 2x = sin(x+x) 3.2 Expand each of the following, using your answer from 3.1: 3.2.1 sin 100° = ..... 3.2.2 sin 46° = .... 3.2.3 sin 40° =. Write the following expressions as a single trigonometric ratio: 3.3.1 2 sin 19° cos 19° = 3.3.2 2 cos 40° sin 40° - 3.3.3 sin 25° cos155° .........​

Answer 1

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.