The image presents a graph with three distinct lines, each representing a different variable, against a white background. The first line is a solid black line, the second line is a solid blue line, and the third line is a solid green line. The x-axis is labeled "input (x)" and the y-axis is labeled "output (y)" with the variable names "x1", "x2", and "x3" on the x-axis and "variable" on the y-axis.