The trigonometric Fourier series expansion of an even function

The trigonometric Fourier series expansion of an even function that is also half-wave symmetric shall contain—

1. odd harmonics of sine terms only
2. both sine and cosine terms
3. only cosine terms
4. only odd harmonics of cosine terms.

In the trigonometric Fourier expansion of an even function that is also half-wave symmetric shall contain only odd harmonics of cosine terms.