17.43 USE problems
condition: Solve the following equation by the method of reducing the degree. \[ \cos ^{2} x+\cos ^{2} 2 x+\cos ^{2} 3 x+\cos ^{2} 4 x=2 \]
Problems of the USE (Unified State Exam) - equations and inequalities in terms of a parameter, solved both by algebraic methods and geometric ones.