A line in 2-dimensional euclidean space can be determined by the coordinates of any two particular points on the line. Hence four "parameters" are required. Now let’s consider a line given by the usual equation y = mx + c. c, being the intercept on the y-axis, is related to the point (0,c) which requires two numbers to be determined. m, the slope, can be given by the tanθ which requires just one number to be determined. Hence when the line is given by the equation y = mx + c one requires just three parameters and not four as in the first case. Which parameter am I missing? Thanks for any help.