17.43 Use Problems
Condition: Solve the following equation by lowering 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 Inequalites in Terms of A Parameter, Solved Both by Algebraic Methods and Geometric One.