Phnom Penh is the capital city of Cambodia. It serves as the political, economic, and cultural center of the country.
Nicosia: Capital of Cyprus.
Hanoi: Capital of Vietnam.
Dili: Capital of East Timor.
Assertion (A): The sum of the first fifteen terms of the AP $ 21, 18, 15, 12, \dots $ is zero.
Reason (R): The sum of the first $ n $ terms of an AP with first term $ a $ and common difference $ d $ is given by: $ S_n = \frac{n}{2} \left[ a + (n - 1) d \right]. $