Answer:
at x=0 (the origin)
Explanation:
The equation for a proportional relationship is ...
y = kx
The equation of a straight line is ...
y = kx +b . . . . . for some y-intercept b
Comparison to general line
Comparing the proportional relation to the relation for a general line, we see that b=0 in the proportional relation. That is, the y-intercept is at y=0, the origin of the Cartesian coordinate plane.
The graph crosses the x-axis at (0, 0), or x=0.
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Additional comment
In y=kx, the value k is called "the constant of proportionality." It is also the slope of the line on a graph.
In the usual representation of the slope-intercept equation of a line, y=mx+b, the slope of the line is represented by 'm'. In the above, we used 'k' for that purpose, to facilitate comparing the equations.