To solve the equation \(2 \cos x - \cos \frac{1}{2}x = 1\), we can use trigonometric identities and algebraic manipulation.
1. Use the double angle formula: \(\cos x = 2 \cos^2 \frac{x}{2} - 1\).
2. Substitute \(\cos x\) in the equation:
\(2(2 \cos^2 \frac{x}{2} - 1) - \cos \frac{x}{2} = 1\)
3. Simplify the equation:
\(4 \cos^2 \frac{x}{2} - 2 - \cos \frac{x}{2} = 1\)
4. Rearrange to form a quadratic equation in \(\cos \frac{x}{2}\):
\(4 \cos^2 \frac{x}{2} - \cos \frac{x}{2} - 3 = 0\)
5. Let \(u = \cos \frac{x}{2}\). The equation becomes:
\(4u^2 - u - 3 = 0\)
6. Solve the quadratic equation using the quadratic formula:
\(u = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\)
where \(a = 4\), \(b = -1\), \(c = -3\).
\(u = \frac{1 \pm \sqrt{1 + 48}}{8} = \frac{1 \pm 7}{8}\)
7. The solutions for \(u\) are:
\(u = 1\) and \(u = -\frac{3}{4}\).
8. Solve for \(x\):
For \(u = 1\), \(\cos \frac{x}{2} = 1\), so \(\frac{x}{2} = 0\) or \(x = 0\).
For \(u = -\frac{3}{4}\), \(\cos \frac{x}{2} = -\frac{3}{4}\), solve for \(\frac{x}{2}\):
\(\frac{x}{2} = \cos^{-1}(-\frac{3}{4})\), so \(x = 2 \cos^{-1}(-\frac{3}{4})\).
9. Calculate \(x\) for \(\cos^{-1}(-\frac{3}{4})\):
\(x \approx 4.84\).
Thus, the solutions are \(x = 0\) and \(x \approx 4.84\).