Write the equation of y axis.

Answer

To find the equation of the y-axis, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Cartesian Plane**: The Cartesian plane consists of two axes: the x-axis (horizontal) and the y-axis (vertical). The y-axis is where all points have an x-coordinate of 0.

2. **Identify Points on the Y-Axis**: Points on the y-axis can be represented as (0, y), where y can take any real number value. For example, (0, 1), (0, -3), (0, 0), etc.

3. **Observe the X-Coordinate**: Notice that for all points on the y-axis, the x-coordinate (also known as the abscissa) is always 0. This means that no matter what the y-coordinate (or ordinate) is, the x-coordinate remains constant at 0.

4. **Write the Equation**: Since the x-coordinate is always 0 for all points on the y-axis, we can express this relationship as an equation:
\[ x = 0 \]

5. **Conclusion**: Therefore, the equation of the y-axis is:
\[ x = 0 \]