Find the resultant amplitude and phase of a point at which N sinusoidal waves interfere. All the waves have same amplitude A and their phases increase in arithmetic progression of common difference `phi`.

Explanation

To find the resultant amplitude and phase of a point at which \( N \) sinusoidal waves interfere, we can follow these steps:

### Step 1: Understand the Problem
We have \( N \) sinusoidal waves, each with the same amplitude \( A \). The phases of these waves increase in an arithmetic progression with a common difference \( \phi \).

### Step 2: Write the Expression for Each Wave
The \( n \)-th wave can be expressed as:
\[
...