Identify the Function of Line 1: Graph Analysis in Coordinate Plane

To solve this problem, we'll follow these steps:

• Determine if the given line labeled '1' has a positive or negative slope.
• Find out if the line passes through the origin, which implies the y-intercept, $b = 0$.
• Identify the function equation based on the observations.

Now, let's work through each step:
- Observation shows that line '1' in red goes through the origin (intersects at the point (0,0)), confirming that the y-intercept, $b$, is zero.
- Given that this line descends from left to right, the slope $m$ is negative. Therefore, the most likely function representation given the described visual descent is $y = -x$.

Thus, the function describing the line numbered '1' is $y = -x$.