Fundamental Frequency of Fourier Equation in Cosine Form

Note: From y = a cos bt, the frequency f = b/2π
For 5 cos (20πt): f₁ = 20π/2π = 10
For 2 cos (40πt): f₂ = 40π/2π = 20
For cos (80πt): f₃ = 80π/2π = 40
 

fundamental frequency, f₀ = lowest frequency
f₀ = 10       Answer: [ A ]