Two parallel lines are shown in the applet below. [br]What coordinate geometry principle is dynamically being illustrated here? [br]Feel free to move the white points anywhere you'd like![br]Feel free to tamper with the sliders too.
If 2 (non-vertical) parallel lines are drawn in the coordinate plane, their slopes are equal. [br](Note the slope triangle for one line "fits perfectly" adjacent the other line, this implying the lines have the same slope.)