The processor (CPU - Central Processing Unit) is responsible for processing data and executing instructions in a computer system. It performs all calculations and tasks required for operations.
Monitor: Displays the processed data as output.
Keyboard: An input device used to enter data.
Mouse: An input device for navigation and interaction.
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]. $