Construct an angle of `90^@` at the initial point of a given ray and justify the construction.

Explanation

To construct a \(90^\circ\) angle at the initial point of a given ray, follow these steps:

### Step-by-Step Construction

1. **Draw a Ray**: Start by drawing a ray \(OA\) with point \(O\) as the initial point and point \(A\) as any point on the ray.

**Hint**: Use a ruler to draw a straight line from point \(O\) to point \(A\).

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