Real part of cos h (ɑ + iβ) is

1) cos h ɑ cos β

2) cos ɑ cos β

3) cos ɑ cos hβ

4) sin ɑ sin hβ

Solution: (1) cos h ɑ cos β

The real part of cos h (ɑ + iβ) is cos h (ɑ + iβ)

= cos h ɑ + cos h iβ + sin h ɑ sin h iβ

= cos h ɑ cos β + i sin h ɑ sin β

Real part = cos h ɑ cos β