If sin α = $\dfrac{1}{2},$ then the value of 3 cos α - 4 cos³ α is

1. -1

2. 0

3. 1

4. 2

The value of $\dfrac{\text{1 - tan}^2 45°}{\text{1 + tan}^2 45°}$ is equal to

1. tan 60°

2. tan 30°

3. sin 45°

4. tan 0°

If △ABC is right angled at C, then the value of cos (A + B) is

1. 0

2. 1

3. $\dfrac{1}{2}$

4. $\dfrac{\sqrt{3}}{2}$

In the adjoining figure, ABC is a right triangle right angled at B. If AB = 10 cm and ∠C = 30°, then the length of the side BC is

1. $\dfrac{10}{\sqrt{3}}$ cm

2. $10\sqrt{3}$ cm

3. 20 cm

4. 5 cm