1.8.6 Compound and double angle formulae (A-level only)

a.

By writing $\cos 3x\,$ as $cos⁡(2x+x)\cos(2x + x)$ , show that $cos 3x = 4\cos^3 x - 3\cos x$ .

[2]

b.

Solve, for $\leq x \leq 180$ , the equation,

4\cos^3 x - 3\cos x = -0.65

Give your answers to 1 decimal place.

[4]

a.

By writing $\cos 3x\,$ as $cos⁡(2x+x)\cos(2x + x)$ , show that $cos 3x = 4\cos^3 x - 3\cos x$ .

[2]

b.

Solve, for $\leq x \leq 180$ , the equation,

4\cos^3 x - 3\cos x = -0.65

Give your answers to 1 decimal place.

[4]

1.8.6 Compound and double angle formulae (A-level only) Questions