# How to plot a vertical line with fixed range? [duplicate]

I want to plot a vertical line on a graph. The plot range on the graph ranges from 0 - 12. I want the vertical line at x-axis = 0.8, but the vertical height going from 0 to 7 only. I am not sure how to do this. I tried with gridlines but there seems no easy way around that.

You can use the option Epilog or Prolog to add graphics primitives (lines, points, texts, etc.) to your plot:
Plot[2 Pi + 2 Pi x Sin[6 Pi x], {x, 0, 1},

Plot[2 Pi + 2 Pi x Sin[6 Pi x], {x, 0, 1},