Correct choice is (b) 0.1
Explanation: X (t) = 10 cos^2 (10 πt)
Since, cos 2t = 2cos^2 t – 1
Or, cos^2 t = \(\frac{1+cos2t}{2}\)
∴ X (t) = 5 + 5 cos 20πt
Now, Y (t) = cos 20πt
Fundamental period of the signal is = \(\frac{2π}{20π} = \frac{1}{10}\) = 0.1.