A straight line shows a direct proportion because each x-value has one y-value, and there is a correlation between the two values, not just random placement. Hope this helps! :)
A straight line on the graph shows two factor that are represented on the x-axis and y-axis is directly proportional to each other.
In this condition the graph between these terms is a straight line. The term directly proportional states that if one factor is increasing then the other factor will also increase.
Example : Ohm's law, a straight line is formed when a graph is made between voltage and current as V=IR
