Challenging +1.2 This is a standard Further Maths FP2 question testing de Moivre's theorem application. Part (a) requires expanding (cos θ + i sin θ)^5 using binomial theorem and equating real parts—a routine technique. Part (b) involves recognizing that cos 5θ = -1 leads to specific angles, then substituting back—methodical but not requiring novel insight. The multi-step nature and Further Maths content places it above average difficulty, but it's a textbook exercise type.