## Subject:

**Problem**

Given the Fourier equation:

*f*(

*t*) = 5 cos (20π

*t*) + 2 cos (40π

*t*) + cos (80π

*t*)

What is the fundamental frequency?

A. 10 | C. 40 |

B. 20 | D. 30 |

**Answer Key**

[ A ]

**Solution**

Note: From

For 5 cos (20π

For 2 cos (40π

For cos (80π

*y*=*a*cos*bt*, the frequency*f*=*b*/2πFor 5 cos (20π

*t*):*f*_{1}= 20π/2π = 10For 2 cos (40π

*t*):*f*_{2}= 40π/2π = 20For cos (80π

*t*):*f*_{3}= 80π/2π = 40fundamental frequency, *f*_{0} = lowest frequency*f*_{0} = 10 Answer: [ A ]